Provided by: fio_3.28-1_amd64 
NAME
fio - flexible I/O tester
SYNOPSIS
fio [options] [jobfile]...
DESCRIPTION
fio is a tool that will spawn a number of threads or processes doing a particular type of I/O action as
specified by the user. The typical use of fio is to write a job file matching the I/O load one wants to
simulate.
OPTIONS
--debug=type
Enable verbose tracing type of various fio actions. May be `all' for all types or individual types
separated by a comma (e.g. `--debug=file,mem' will enable file and memory debugging). `help' will
list all available tracing options.
--parse-only
Parse options only, don't start any I/O.
--merge-blktrace-only
Merge blktraces only, don't start any I/O.
--output=filename
Write output to filename.
--output-format=format
Set the reporting format to `normal', `terse', `json', or `json+'. Multiple formats can be
selected, separate by a comma. `terse' is a CSV based format. `json+' is like `json', except it
adds a full dump of the latency buckets.
--bandwidth-log
Generate aggregate bandwidth logs.
--minimal
Print statistics in a terse, semicolon-delimited format.
--append-terse
Print statistics in selected mode AND terse, semicolon-delimited format. Deprecated, use
--output-format instead to select multiple formats.
--terse-version=version
Set terse version output format (default `3', or `2', `4', `5').
--version
Print version information and exit.
--help Print a summary of the command line options and exit.
--cpuclock-test
Perform test and validation of internal CPU clock.
--crctest=[test]
Test the speed of the built-in checksumming functions. If no argument is given, all of them are
tested. Alternatively, a comma separated list can be passed, in which case the given ones are
tested.
--cmdhelp=command
Print help information for command. May be `all' for all commands.
--enghelp=[ioengine[,command]]
List all commands defined by ioengine, or print help for command defined by ioengine. If no
ioengine is given, list all available ioengines.
--showcmd=jobfile
Convert jobfile to a set of command-line options.
--readonly
Turn on safety read-only checks, preventing writes and trims. The --readonly option is an extra
safety guard to prevent users from accidentally starting a write or trim workload when that is not
desired. Fio will only modify the device under test if
`rw=write/randwrite/rw/randrw/trim/randtrim/trimwrite' is given. This safety net can be used as an
extra precaution.
--eta=when
Specifies when real-time ETA estimate should be printed. when may be `always', `never' or `auto'.
`auto' is the default, it prints ETA when requested if the output is a TTY. `always' disregards
the output type, and prints ETA when requested. `never' never prints ETA.
--eta-interval=time
By default, fio requests client ETA status roughly every second. With this option, the interval is
configurable. Fio imposes a minimum allowed time to avoid flooding the console, less than 250 msec
is not supported.
--eta-newline=time
Force a new line for every time period passed. When the unit is omitted, the value is interpreted
in seconds.
--status-interval=time
Force a full status dump of cumulative (from job start) values at time intervals. This option does
*not* provide per-period measurements. So values such as bandwidth are running averages. When the
time unit is omitted, time is interpreted in seconds. Note that using this option with `--output-
format=json' will yield output that technically isn't valid json, since the output will be
collated sets of valid json. It will need to be split into valid sets of json after the run.
--section=name
Only run specified section name in job file. Multiple sections can be specified. The --section
option allows one to combine related jobs into one file. E.g. one job file could define light,
moderate, and heavy sections. Tell fio to run only the "heavy" section by giving `--section=heavy'
command line option. One can also specify the "write" operations in one section and "verify"
operation in another section. The --section option only applies to job sections. The reserved
*global* section is always parsed and used.
--alloc-size=kb
Allocate additional internal smalloc pools of size kb in KiB. The --alloc-size option increases
shared memory set aside for use by fio. If running large jobs with randommap enabled, fio can run
out of memory. Smalloc is an internal allocator for shared structures from a fixed size memory
pool and can grow to 16 pools. The pool size defaults to 16MiB. NOTE: While running
`.fio_smalloc.*' backing store files are visible in `/tmp'.
--warnings-fatal
All fio parser warnings are fatal, causing fio to exit with an error.
--max-jobs=nr
Set the maximum number of threads/processes to support to nr. NOTE: On Linux, it may be necessary
to increase the shared-memory limit (`/proc/sys/kernel/shmmax') if fio runs into errors while
creating jobs.
--server=args
Start a backend server, with args specifying what to listen to. See CLIENT/SERVER section.
--daemonize=pidfile
Background a fio server, writing the pid to the given pidfile file.
--client=hostname
Instead of running the jobs locally, send and run them on the given hostname or set of hostnames.
See CLIENT/SERVER section.
--remote-config=file
Tell fio server to load this local file.
--idle-prof=option
Report CPU idleness. option is one of the following:
calibrate
Run unit work calibration only and exit.
system Show aggregate system idleness and unit work.
percpu As system but also show per CPU idleness.
--inflate-log=log
Inflate and output compressed log.
--trigger-file=file
Execute trigger command when file exists.
--trigger-timeout=time
Execute trigger at this time.
--trigger=command
Set this command as local trigger.
--trigger-remote=command
Set this command as remote trigger.
--aux-path=path
Use the directory specified by path for generated state files instead of the current working
directory.
JOB FILE FORMAT
Any parameters following the options will be assumed to be job files, unless they match a job file
parameter. Multiple job files can be listed and each job file will be regarded as a separate group. Fio
will stonewall execution between each group.
Fio accepts one or more job files describing what it is supposed to do. The job file format is the
classic ini file, where the names enclosed in [] brackets define the job name. You are free to use any
ASCII name you want, except *global* which has special meaning. Following the job name is a sequence of
zero or more parameters, one per line, that define the behavior of the job. If the first character in a
line is a ';' or a '#', the entire line is discarded as a comment.
A *global* section sets defaults for the jobs described in that file. A job may override a *global*
section parameter, and a job file may even have several *global* sections if so desired. A job is only
affected by a *global* section residing above it.
The --cmdhelp option also lists all options. If used with an command argument, --cmdhelp will detail the
given command.
See the `examples/' directory for inspiration on how to write job files. Note the copyright and license
requirements currently apply to `examples/' files.
Note that the maximum length of a line in the job file is 8192 bytes.
JOB FILE PARAMETERS
Some parameters take an option of a given type, such as an integer or a string. Anywhere a numeric value
is required, an arithmetic expression may be used, provided it is surrounded by parentheses. Supported
operators are:
addition (+)
subtraction (-)
multiplication (*)
division (/)
modulus (%)
exponentiation (^)
For time values in expressions, units are microseconds by default. This is different than for time values
not in expressions (not enclosed in parentheses).
PARAMETER TYPES
The following parameter types are used.
str String. A sequence of alphanumeric characters.
time Integer with possible time suffix. Without a unit value is interpreted as seconds unless otherwise
specified. Accepts a suffix of 'd' for days, 'h' for hours, 'm' for minutes, 's' for seconds, 'ms'
(or 'msec') for milliseconds and 'us' (or 'usec') for microseconds. For example, use 10m for 10
minutes.
int Integer. A whole number value, which may contain an integer prefix and an integer suffix.
[*integer prefix*] **number** [*integer suffix*]
The optional *integer prefix* specifies the number's base. The default is decimal. *0x* specifies
hexadecimal.
The optional *integer suffix* specifies the number's units, and includes an optional unit prefix
and an optional unit. For quantities of data, the default unit is bytes. For quantities of time,
the default unit is seconds unless otherwise specified.
With `kb_base=1000', fio follows international standards for unit prefixes. To specify power-of-10
decimal values defined in the International System of Units (SI):
K means kilo (K) or 1000
M means mega (M) or 1000**2
G means giga (G) or 1000**3
T means tera (T) or 1000**4
P means peta (P) or 1000**5
To specify power-of-2 binary values defined in IEC 80000-13:
Ki means kibi (Ki) or 1024
Mi means mebi (Mi) or 1024**2
Gi means gibi (Gi) or 1024**3
Ti means tebi (Ti) or 1024**4
Pi means pebi (Pi) or 1024**5
For Zone Block Device Mode:
z means Zone
With `kb_base=1024' (the default), the unit prefixes are opposite from those specified in the SI
and IEC 80000-13 standards to provide compatibility with old scripts. For example, 4k means 4096.
For quantities of data, an optional unit of 'B' may be included (e.g., 'kB' is the same as 'k').
The *integer suffix* is not case sensitive (e.g., m/mi mean mebi/mega, not milli). 'b' and 'B'
both mean byte, not bit.
Examples with `kb_base=1000':
4 KiB: 4096, 4096b, 4096B, 4k, 4kb, 4kB, 4K, 4KB
1 MiB: 1048576, 1m, 1024k
1 MB: 1000000, 1mi, 1000ki
1 TiB: 1073741824, 1t, 1024m, 1048576k
1 TB: 1000000000, 1ti, 1000mi, 1000000ki
Examples with `kb_base=1024' (default):
4 KiB: 4096, 4096b, 4096B, 4k, 4kb, 4kB, 4K, 4KB
1 MiB: 1048576, 1m, 1024k
1 MB: 1000000, 1mi, 1000ki
1 TiB: 1073741824, 1t, 1024m, 1048576k
1 TB: 1000000000, 1ti, 1000mi, 1000000ki
To specify times (units are not case sensitive):
D means days
H means hours
M mean minutes
s or sec means seconds (default)
ms or msec means milliseconds
us or usec means microseconds
`z' suffix specifies that the value is measured in zones. Value is recalculated once block
device's zone size becomes known.
If the option accepts an upper and lower range, use a colon ':' or minus '-' to separate such
values. See irange parameter type. If the lower value specified happens to be larger than the
upper value the two values are swapped.
bool Boolean. Usually parsed as an integer, however only defined for true and false (1 and 0).
irange Integer range with suffix. Allows value range to be given, such as 1024-4096. A colon may also be
used as the separator, e.g. 1k:4k. If the option allows two sets of ranges, they can be specified
with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see int parameter type.
float_list
A list of floating point numbers, separated by a ':' character.
JOB PARAMETERS
With the above in mind, here follows the complete list of fio job parameters.
Units
kb_base=int
Select the interpretation of unit prefixes in input parameters.
1000 Inputs comply with IEC 80000-13 and the International System of Units (SI). Use:
- power-of-2 values with IEC prefixes (e.g., KiB)
- power-of-10 values with SI prefixes (e.g., kB)
1024 Compatibility mode (default). To avoid breaking old scripts:
- power-of-2 values with SI prefixes
- power-of-10 values with IEC prefixes
See bs for more details on input parameters.
Outputs always use correct prefixes. Most outputs include both side-by-side, like:
bw=2383.3kB/s (2327.4KiB/s)
If only one value is reported, then kb_base selects the one to use:
1000 -- SI prefixes
1024 -- IEC prefixes
unit_base=int
Base unit for reporting. Allowed values are:
0 Use auto-detection (default).
8 Byte based.
1 Bit based.
Job description
name=str
ASCII name of the job. This may be used to override the name printed by fio for this job.
Otherwise the job name is used. On the command line this parameter has the special purpose of also
signaling the start of a new job.
description=str
Text description of the job. Doesn't do anything except dump this text description when this job
is run. It's not parsed.
loops=int
Run the specified number of iterations of this job. Used to repeat the same workload a given
number of times. Defaults to 1.
numjobs=int
Create the specified number of clones of this job. Each clone of job is spawned as an independent
thread or process. May be used to setup a larger number of threads/processes doing the same thing.
Each thread is reported separately; to see statistics for all clones as a whole, use
group_reporting in conjunction with new_group. See --max-jobs. Default: 1.
Time related parameters
runtime=time
Tell fio to terminate processing after the specified period of time. It can be quite hard to
determine for how long a specified job will run, so this parameter is handy to cap the total
runtime to a given time. When the unit is omitted, the value is interpreted in seconds.
time_based
If set, fio will run for the duration of the runtime specified even if the file(s) are completely
read or written. It will simply loop over the same workload as many times as the runtime allows.
startdelay=irange(int)
Delay the start of job for the specified amount of time. Can be a single value or a range. When
given as a range, each thread will choose a value randomly from within the range. Value is in
seconds if a unit is omitted.
ramp_time=time
If set, fio will run the specified workload for this amount of time before logging any performance
numbers. Useful for letting performance settle before logging results, thus minimizing the runtime
required for stable results. Note that the ramp_time is considered lead in time for a job, thus it
will increase the total runtime if a special timeout or runtime is specified. When the unit is
omitted, the value is given in seconds.
clocksource=str
Use the given clocksource as the base of timing. The supported options are:
gettimeofday
gettimeofday(2)
clock_gettime
clock_gettime(2)
cpu Internal CPU clock source
cpu is the preferred clocksource if it is reliable, as it is very fast (and fio is heavy on time
calls). Fio will automatically use this clocksource if it's supported and considered reliable on
the system it is running on, unless another clocksource is specifically set. For x86/x86-64 CPUs,
this means supporting TSC Invariant.
gtod_reduce=bool
Enable all of the gettimeofday(2) reducing options (disable_clat, disable_slat,
disable_bw_measurement) plus reduce precision of the timeout somewhat to really shrink the
gettimeofday(2) call count. With this option enabled, we only do about 0.4% of the gettimeofday(2)
calls we would have done if all time keeping was enabled.
gtod_cpu=int
Sometimes it's cheaper to dedicate a single thread of execution to just getting the current time.
Fio (and databases, for instance) are very intensive on gettimeofday(2) calls. With this option,
you can set one CPU aside for doing nothing but logging current time to a shared memory location.
Then the other threads/processes that run I/O workloads need only copy that segment, instead of
entering the kernel with a gettimeofday(2) call. The CPU set aside for doing these time calls will
be excluded from other uses. Fio will manually clear it from the CPU mask of other jobs.
Target file/device
directory=str
Prefix filenames with this directory. Used to place files in a different location than `./'. You
can specify a number of directories by separating the names with a ':' character. These
directories will be assigned equally distributed to job clones created by numjobs as long as they
are using generated filenames. If specific filename(s) are set fio will use the first listed
directory, and thereby matching the filename semantic (which generates a file for each clone if
not specified, but lets all clones use the same file if set).
See the filename option for information on how to escape ':' characters within the directory path
itself.
Note: To control the directory fio will use for internal state files use --aux-path.
filename=str
Fio normally makes up a filename based on the job name, thread number, and file number (see
filename_format). If you want to share files between threads in a job or several jobs with fixed
file paths, specify a filename for each of them to override the default. If the ioengine is file
based, you can specify a number of files by separating the names with a ':' colon. So if you
wanted a job to open `/dev/sda' and `/dev/sdb' as the two working files, you would use
`filename=/dev/sda:/dev/sdb'. This also means that whenever this option is specified, nrfiles is
ignored. The size of regular files specified by this option will be size divided by number of
files unless an explicit size is specified by filesize.
Each colon in the wanted path must be escaped with a '\' character. For instance, if the path is
`/dev/dsk/foo@3,0:c' then you would use `filename=/dev/dsk/foo@3,0\:c' and if the path is
`F:\filename' then you would use `filename=F\:\filename'.
On Windows, disk devices are accessed as `\\.\PhysicalDrive0' for the first device,
`\\.\PhysicalDrive1' for the second etc. Note: Windows and FreeBSD prevent write access to areas
of the disk containing in-use data (e.g. filesystems).
The filename `-' is a reserved name, meaning *stdin* or *stdout*. Which of the two depends on the
read/write direction set.
filename_format=str
If sharing multiple files between jobs, it is usually necessary to have fio generate the exact
names that you want. By default, fio will name a file based on the default file format
specification of `jobname.jobnumber.filenumber'. With this option, that can be customized. Fio
will recognize and replace the following keywords in this string:
$jobname
The name of the worker thread or process.
$clientuid
IP of the fio process when using client/server mode.
$jobnum
The incremental number of the worker thread or process.
$filenum
The incremental number of the file for that worker thread or process.
To have dependent jobs share a set of files, this option can be set to have fio generate filenames
that are shared between the two. For instance, if `testfiles.$filenum' is specified, file number 4
for any job will be named `testfiles.4'. The default of `$jobname.$jobnum.$filenum' will be used
if no other format specifier is given.
If you specify a path then the directories will be created up to the main directory for the file.
So for example if you specify `a/b/c/$jobnum` then the directories a/b/c will be created before
the file setup part of the job. If you specify directory then the path will be relative that
directory, otherwise it is treated as the absolute path.
unique_filename=bool
To avoid collisions between networked clients, fio defaults to prefixing any generated filenames
(with a directory specified) with the source of the client connecting. To disable this behavior,
set this option to 0.
opendir=str
Recursively open any files below directory str.
lockfile=str
Fio defaults to not locking any files before it does I/O to them. If a file or file descriptor is
shared, fio can serialize I/O to that file to make the end result consistent. This is usual for
emulating real workloads that share files. The lock modes are:
none No locking. The default.
exclusive
Only one thread or process may do I/O at a time, excluding all others.
readwrite
Read-write locking on the file. Many readers may access the file at the same time,
but writes get exclusive access.
nrfiles=int
Number of files to use for this job. Defaults to 1. The size of files will be size divided by this
unless explicit size is specified by filesize. Files are created for each thread separately, and
each file will have a file number within its name by default, as explained in filename section.
openfiles=int
Number of files to keep open at the same time. Defaults to the same as nrfiles, can be set smaller
to limit the number simultaneous opens.
file_service_type=str
Defines how fio decides which file from a job to service next. The following types are defined:
random Choose a file at random.
roundrobin
Round robin over opened files. This is the default.
sequential
Finish one file before moving on to the next. Multiple files can still be open
depending on openfiles.
zipf Use a Zipf distribution to decide what file to access.
pareto Use a Pareto distribution to decide what file to access.
normal Use a Gaussian (normal) distribution to decide what file to access.
gauss Alias for normal.
For random, roundrobin, and sequential, a postfix can be appended to tell fio how many I/Os to
issue before switching to a new file. For example, specifying `file_service_type=random:8' would
cause fio to issue 8 I/Os before selecting a new file at random. For the non-uniform
distributions, a floating point postfix can be given to influence how the distribution is skewed.
See random_distribution for a description of how that would work.
ioscheduler=str
Attempt to switch the device hosting the file to the specified I/O scheduler before running. If
the file is a pipe, a character device file or if device hosting the file could not be determined,
this option is ignored.
create_serialize=bool
If true, serialize the file creation for the jobs. This may be handy to avoid interleaving of data
files, which may greatly depend on the filesystem used and even the number of processors in the
system. Default: true.
create_fsync=bool
fsync(2) the data file after creation. This is the default.
create_on_open=bool
If true, don't pre-create files but allow the job's open() to create a file when it's time to do
I/O. Default: false -- pre-create all necessary files when the job starts.
create_only=bool
If true, fio will only run the setup phase of the job. If files need to be laid out or updated on
disk, only that will be done -- the actual job contents are not executed. Default: false.
allow_file_create=bool
If true, fio is permitted to create files as part of its workload. If this option is false, then
fio will error out if the files it needs to use don't already exist. Default: true.
allow_mounted_write=bool
If this isn't set, fio will abort jobs that are destructive (e.g. that write) to what appears to
be a mounted device or partition. This should help catch creating inadvertently destructive tests,
not realizing that the test will destroy data on the mounted file system. Note that some platforms
don't allow writing against a mounted device regardless of this option. Default: false.
pre_read=bool
If this is given, files will be pre-read into memory before starting the given I/O operation. This
will also clear the invalidate flag, since it is pointless to pre-read and then drop the cache.
This will only work for I/O engines that are seek-able, since they allow you to read the same data
multiple times. Thus it will not work on non-seekable I/O engines (e.g. network, splice). Default:
false.
unlink=bool
Unlink the job files when done. Not the default, as repeated runs of that job would then waste
time recreating the file set again and again. Default: false.
unlink_each_loop=bool
Unlink job files after each iteration or loop. Default: false.
zonemode=str
Accepted values are:
none The zonerange, zonesize zonecapacity and zoneskip parameters are ignored.
strided
I/O happens in a single zone until zonesize bytes have been transferred. After that
number of bytes has been transferred processing of the next zone starts. The
zonecapacity parameter is ignored.
zbd Zoned block device mode. I/O happens sequentially in each zone, even if random I/O
has been selected. Random I/O happens across all zones instead of being restricted
to a single zone. Trim is handled using a zone reset operation. Trim only considers
non-empty sequential write required and sequential write preferred zones.
zonerange=int
For zonemode=strided, this is the size of a single zone. See also zonesize and zoneskip.
For zonemode=zbd, this parameter is ignored.
zonesize=int
For zonemode=strided, this is the number of bytes to transfer before skipping zoneskip bytes. If
this parameter is smaller than zonerange then only a fraction of each zone with zonerange bytes
will be accessed. If this parameter is larger than zonerange then each zone will be accessed
multiple times before skipping to the next zone.
For zonemode=zbd, this is the size of a single zone. The zonerange parameter is ignored in this
mode. For a job accessing a zoned block device, the specified zonesize must be 0 or equal to the
device zone size. For a regular block device or file, the specified zonesize must be at least
512B.
zonecapacity=int
For zonemode=zbd, this defines the capacity of a single zone, which is the accessible area
starting from the zone start address. This parameter only applies when using zonemode=zbd in
combination with regular block devices. If not specified it defaults to the zone size. If the
target device is a zoned block device, the zone capacity is obtained from the device information
and this option is ignored.
zoneskip=int[z]
For zonemode=strided, the number of bytes to skip after zonesize bytes of data have been
transferred.
For zonemode=zbd, the zonesize aligned number of bytes to skip once a zone is fully written (write
workloads) or all written data in the zone have been read (read workloads). This parameter is
valid only for sequential workloads and ignored for random workloads. For read workloads, see also
read_beyond_wp.
read_beyond_wp=bool
This parameter applies to zonemode=zbd only.
Zoned block devices are block devices that consist of multiple zones. Each zone has a type, e.g.
conventional or sequential. A conventional zone can be written at any offset that is a multiple of
the block size. Sequential zones must be written sequentially. The position at which a write must
occur is called the write pointer. A zoned block device can be either host managed or host aware.
For host managed devices the host must ensure that writes happen sequentially. Fio recognizes host
managed devices and serializes writes to sequential zones for these devices.
If a read occurs in a sequential zone beyond the write pointer then the zoned block device will
complete the read without reading any data from the storage medium. Since such reads lead to
unrealistically high bandwidth and IOPS numbers fio only reads beyond the write pointer if
explicitly told to do so. Default: false.
max_open_zones=int
When running a random write test across an entire drive many more zones will be open than in a
typical application workload. Hence this command line option that allows to limit the number of
open zones. The number of open zones is defined as the number of zones to which write commands are
issued by all threads/processes.
job_max_open_zones=int
Limit on the number of simultaneously opened zones per single thread/process.
ignore_zone_limits=bool
If this isn't set, fio will query the max open zones limit from the zoned block device, and exit
if the specified max_open_zones value is larger than the limit reported by the device. Default:
false.
zone_reset_threshold=float
A number between zero and one that indicates the ratio of logical blocks with data to the total
number of logical blocks in the test above which zones should be reset periodically.
zone_reset_frequency=float
A number between zero and one that indicates how often a zone reset should be issued if the zone
reset threshold has been exceeded. A zone reset is submitted after each (1 / zone_reset_frequency)
write requests. This and the previous parameter can be used to simulate garbage collection
activity.
I/O type
direct=bool
If value is true, use non-buffered I/O. This is usually O_DIRECT. Note that OpenBSD and ZFS on
Solaris don't support direct I/O. On Windows the synchronous ioengines don't support direct I/O.
Default: false.
atomic=bool
If value is true, attempt to use atomic direct I/O. Atomic writes are guaranteed to be stable once
acknowledged by the operating system. Only Linux supports O_ATOMIC right now.
buffered=bool
If value is true, use buffered I/O. This is the opposite of the direct option. Defaults to true.
readwrite=str, rw=str
Type of I/O pattern. Accepted values are:
read Sequential reads.
write Sequential writes.
trim Sequential trims (Linux block devices and SCSI character devices only).
randread
Random reads.
randwrite
Random writes.
randtrim
Random trims (Linux block devices and SCSI character devices only).
rw,readwrite
Sequential mixed reads and writes.
randrw Random mixed reads and writes.
trimwrite
Sequential trim+write sequences. Blocks will be trimmed first, then the same blocks
will be written to.
Fio defaults to read if the option is not specified. For the mixed I/O types, the default is to
split them 50/50. For certain types of I/O the result may still be skewed a bit, since the speed
may be different.
It is possible to specify the number of I/Os to do before getting a new offset by appending
`:<nr>' to the end of the string given. For a random read, it would look like `rw=randread:8' for
passing in an offset modifier with a value of 8. If the suffix is used with a sequential I/O
pattern, then the `<nr>' value specified will be added to the generated offset for each I/O
turning sequential I/O into sequential I/O with holes. For instance, using `rw=write:4k' will
skip 4k for every write. Also see the rw_sequencer option.
rw_sequencer=str
If an offset modifier is given by appending a number to the `rw=str' line, then this option
controls how that number modifies the I/O offset being generated. Accepted values are:
sequential
Generate sequential offset.
identical
Generate the same offset.
sequential is only useful for random I/O, where fio would normally generate a new random offset
for every I/O. If you append e.g. 8 to randread, you would get a new random offset for every 8
I/Os. The result would be a seek for only every 8 I/Os, instead of for every I/O. Use
`rw=randread:8' to specify that. As sequential I/O is already sequential, setting sequential for
that would not result in any differences. identical behaves in a similar fashion, except it sends
the same offset 8 number of times before generating a new offset.
unified_rw_reporting=str
Fio normally reports statistics on a per data direction basis, meaning that reads, writes, and
trims are accounted and reported separately. This option determines whether fio reports the
results normally, summed together, or as both options. Accepted values are:
none Normal statistics reporting.
mixed Statistics are summed per data direction and reported together.
both Statistics are reported normally, followed by the mixed statistics.
0 Backward-compatible alias for none.
1 Backward-compatible alias for mixed.
2 Alias for both.
randrepeat=bool
Seed the random number generator used for random I/O patterns in a predictable way so the pattern
is repeatable across runs. Default: true.
allrandrepeat=bool
Seed all random number generators in a predictable way so results are repeatable across runs.
Default: false.
randseed=int
Seed the random number generators based on this seed value, to be able to control what sequence of
output is being generated. If not set, the random sequence depends on the randrepeat setting.
fallocate=str
Whether pre-allocation is performed when laying down files. Accepted values are:
none Do not pre-allocate space.
native Use a platform's native pre-allocation call but fall back to none behavior if it
fails/is not implemented.
posix Pre-allocate via posix_fallocate(3).
keep Pre-allocate via fallocate(2) with FALLOC_FL_KEEP_SIZE set.
truncate
Extend file to final size using ftruncate|(2) instead of allocating.
0 Backward-compatible alias for none.
1 Backward-compatible alias for posix.
May not be available on all supported platforms. keep is only available on Linux. If using ZFS on
Solaris this cannot be set to posix because ZFS doesn't support pre-allocation. Default: native if
any pre-allocation methods except truncate are available, none if not.
Note that using truncate on Windows will interact surprisingly with non-sequential write patterns.
When writing to a file that has been extended by setting the end-of-file information, Windows will
backfill the unwritten portion of the file up to that offset with zeroes before issuing the new
write. This means that a single small write to the end of an extended file will stall until the
entire file has been filled with zeroes.
fadvise_hint=str
Use posix_fadvise(2) or posix_madvise(2) to advise the kernel what I/O patterns are likely to be
issued. Accepted values are:
0 Backwards compatible hint for "no hint".
1 Backwards compatible hint for "advise with fio workload type". This uses FADV_RANDOM
for a random workload, and FADV_SEQUENTIAL for a sequential workload.
sequential
Advise using FADV_SEQUENTIAL.
random Advise using FADV_RANDOM.
write_hint=str
Use fcntl(2) to advise the kernel what life time to expect from a write. Only supported on Linux,
as of version 4.13. Accepted values are:
none No particular life time associated with this file.
short Data written to this file has a short life time.
medium Data written to this file has a medium life time.
long Data written to this file has a long life time.
extreme
Data written to this file has a very long life time.
The values are all relative to each other, and no absolute meaning should be associated with them.
offset=int[%|z]
Start I/O at the provided offset in the file, given as either a fixed size in bytes, zones or a
percentage. If a percentage is given, the generated offset will be aligned to the minimum
blocksize or to the value of offset_align if provided. Data before the given offset will not be
touched. This effectively caps the file size at `real_size - offset'. Can be combined with size to
constrain the start and end range of the I/O workload. A percentage can be specified by a number
between 1 and 100 followed by '%', for example, `offset=20%' to specify 20%. In ZBD mode, value
can be set as number of zones using 'z'.
offset_align=int
If set to non-zero value, the byte offset generated by a percentage offset is aligned upwards to
this value. Defaults to 0 meaning that a percentage offset is aligned to the minimum block size.
offset_increment=int[%|z]
If this is provided, then the real offset becomes `offset + offset_increment * thread_number',
where the thread number is a counter that starts at 0 and is incremented for each sub-job (i.e.
when numjobs option is specified). This option is useful if there are several jobs which are
intended to operate on a file in parallel disjoint segments, with even spacing between the
starting points. Percentages can be used for this option. If a percentage is given, the generated
offset will be aligned to the minimum blocksize or to the value of offset_align if provided.In ZBD
mode, value can be set as number of zones using 'z'.
number_ios=int
Fio will normally perform I/Os until it has exhausted the size of the region set by size, or if it
exhaust the allocated time (or hits an error condition). With this setting, the range/size can be
set independently of the number of I/Os to perform. When fio reaches this number, it will exit
normally and report status. Note that this does not extend the amount of I/O that will be done, it
will only stop fio if this condition is met before other end-of-job criteria.
fsync=int
If writing to a file, issue an fsync(2) (or its equivalent) of the dirty data for every number of
blocks given. For example, if you give 32 as a parameter, fio will sync the file after every 32
writes issued. If fio is using non-buffered I/O, we may not sync the file. The exception is the sg
I/O engine, which synchronizes the disk cache anyway. Defaults to 0, which means fio does not
periodically issue and wait for a sync to complete. Also see end_fsync and fsync_on_close.
fdatasync=int
Like fsync but uses fdatasync(2) to only sync data and not metadata blocks. In Windows, FreeBSD,
DragonFlyBSD or OSX there is no fdatasync(2) so this falls back to using fsync(2). Defaults to 0,
which means fio does not periodically issue and wait for a data-only sync to complete.
write_barrier=int
Make every N-th write a barrier write.
sync_file_range=str:int
Use sync_file_range(2) for every int number of write operations. Fio will track range of writes
that have happened since the last sync_file_range(2) call. str can currently be one or more of:
wait_before
SYNC_FILE_RANGE_WAIT_BEFORE
write SYNC_FILE_RANGE_WRITE
wait_after
SYNC_FILE_RANGE_WRITE_AFTER
So if you do `sync_file_range=wait_before,write:8', fio would use `SYNC_FILE_RANGE_WAIT_BEFORE |
SYNC_FILE_RANGE_WRITE' for every 8 writes. Also see the sync_file_range(2) man page. This option
is Linux specific.
overwrite=bool
If true, writes to a file will always overwrite existing data. If the file doesn't already exist,
it will be created before the write phase begins. If the file exists and is large enough for the
specified write phase, nothing will be done. Default: false.
end_fsync=bool
If true, fsync(2) file contents when a write stage has completed. Default: false.
fsync_on_close=bool
If true, fio will fsync(2) a dirty file on close. This differs from end_fsync in that it will
happen on every file close, not just at the end of the job. Default: false.
rwmixread=int
Percentage of a mixed workload that should be reads. Default: 50.
rwmixwrite=int
Percentage of a mixed workload that should be writes. If both rwmixread and rwmixwrite is given
and the values do not add up to 100%, the latter of the two will be used to override the first.
This may interfere with a given rate setting, if fio is asked to limit reads or writes to a
certain rate. If that is the case, then the distribution may be skewed. Default: 50.
random_distribution=str:float[:float][,str:float][,str:float]
By default, fio will use a completely uniform random distribution when asked to perform random
I/O. Sometimes it is useful to skew the distribution in specific ways, ensuring that some parts of
the data is more hot than others. fio includes the following distribution models:
random Uniform random distribution
zipf Zipf distribution
pareto Pareto distribution
normal Normal (Gaussian) distribution
zoned Zoned random distribution zoned_abs Zoned absolute random distribution
When using a zipf or pareto distribution, an input value is also needed to define the access
pattern. For zipf, this is the `Zipf theta'. For pareto, it's the `Pareto power'. Fio includes a
test program, fio-genzipf, that can be used visualize what the given input values will yield in
terms of hit rates. If you wanted to use zipf with a `theta' of 1.2, you would use
`random_distribution=zipf:1.2' as the option. If a non-uniform model is used, fio will disable use
of the random map. For the normal distribution, a normal (Gaussian) deviation is supplied as a
value between 0 and 100.
The second, optional float is allowed for pareto, zipf and normal distributions. It allows to set
base of distribution in non-default place, giving more control over most probable outcome. This
value is in range [0-1] which maps linearly to range of possible random values. Defaults are:
random for pareto and zipf, and 0.5 for normal. If you wanted to use zipf with a `theta` of 1.2
centered on 1/4 of allowed value range, you would use `random_distibution=zipf:1.2:0.25`.
For a zoned distribution, fio supports specifying percentages of I/O access that should fall
within what range of the file or device. For example, given a criteria of:
60% of accesses should be to the first 10%
30% of accesses should be to the next 20%
8% of accesses should be to the next 30%
2% of accesses should be to the next 40%
we can define that through zoning of the random accesses. For the above example, the user would
do:
random_distribution=zoned:60/10:30/20:8/30:2/40
A zoned_abs distribution works exactly like thezoned, except that it takes absolute sizes. For
example, let's say you wanted to define access according to the following criteria:
60% of accesses should be to the first 20G
30% of accesses should be to the next 100G
10% of accesses should be to the next 500G
we can define an absolute zoning distribution with:
random_distribution=zoned:60/10:30/20:8/30:2/40
For both zoned and zoned_abs, fio supports defining up to 256 separate zones.
Similarly to how bssplit works for setting ranges and percentages of block sizes. Like bssplit,
it's possible to specify separate zones for reads, writes, and trims. If just one set is given,
it'll apply to all of them.
percentage_random=int[,int][,int]
For a random workload, set how big a percentage should be random. This defaults to 100%, in which
case the workload is fully random. It can be set from anywhere from 0 to 100. Setting it to 0
would make the workload fully sequential. Any setting in between will result in a random mix of
sequential and random I/O, at the given percentages. Comma-separated values may be specified for
reads, writes, and trims as described in blocksize.
norandommap
Normally fio will cover every block of the file when doing random I/O. If this option is given,
fio will just get a new random offset without looking at past I/O history. This means that some
blocks may not be read or written, and that some blocks may be read/written more than once. If
this option is used with verify and multiple blocksizes (via bsrange), only intact blocks are
verified, i.e., partially-overwritten blocks are ignored. With an async I/O engine and an I/O
depth > 1, it is possible for the same block to be overwritten, which can cause verification
errors. Either do not use norandommap in this case, or also use the lfsr random generator.
softrandommap=bool
See norandommap. If fio runs with the random block map enabled and it fails to allocate the map,
if this option is set it will continue without a random block map. As coverage will not be as
complete as with random maps, this option is disabled by default.
random_generator=str
Fio supports the following engines for generating I/O offsets for random I/O:
tausworthe
Strong 2^88 cycle random number generator.
lfsr Linear feedback shift register generator.
tausworthe64
Strong 64-bit 2^258 cycle random number generator.
tausworthe is a strong random number generator, but it requires tracking on the side if we want to
ensure that blocks are only read or written once. lfsr guarantees that we never generate the same
offset twice, and it's also less computationally expensive. It's not a true random generator,
however, though for I/O purposes it's typically good enough. lfsr only works with single block
sizes, not with workloads that use multiple block sizes. If used with such a workload, fio may
read or write some blocks multiple times. The default value is tausworthe, unless the required
space exceeds 2^32 blocks. If it does, then tausworthe64 is selected automatically.
Block size
blocksize=int[,int][,int], bs=int[,int][,int]
The block size in bytes used for I/O units. Default: 4096. A single value applies to reads,
writes, and trims. Comma-separated values may be specified for reads, writes, and trims. A value
not terminated in a comma applies to subsequent types. Examples:
bs=256k means 256k for reads, writes and trims.
bs=8k,32k means 8k for reads, 32k for writes and trims.
bs=8k,32k, means 8k for reads, 32k for writes, and default for trims.
bs=,8k means default for reads, 8k for writes and trims.
bs=,8k, means default for reads, 8k for writes, and default for trims.
blocksize_range=irange[,irange][,irange], bsrange=irange[,irange][,irange]
A range of block sizes in bytes for I/O units. The issued I/O unit will always be a multiple of
the minimum size, unless blocksize_unaligned is set. Comma-separated ranges may be specified for
reads, writes, and trims as described in blocksize. Example:
bsrange=1k-4k,2k-8k
bssplit=str[,str][,str]
Sometimes you want even finer grained control of the block sizes issued, not just an even split
between them. This option allows you to weight various block sizes, so that you are able to define
a specific amount of block sizes issued. The format for this option is:
bssplit=blocksize/percentage:blocksize/percentage
for as many block sizes as needed. So if you want to define a workload that has 50% 64k blocks,
10% 4k blocks, and 40% 32k blocks, you would write:
bssplit=4k/10:64k/50:32k/40
Ordering does not matter. If the percentage is left blank, fio will fill in the remaining values
evenly. So a bssplit option like this one:
bssplit=4k/50:1k/:32k/
would have 50% 4k ios, and 25% 1k and 32k ios. The percentages always add up to 100, if bssplit is
given a range that adds up to more, it will error out.
Comma-separated values may be specified for reads, writes, and trims as described in blocksize.
If you want a workload that has 50% 2k reads and 50% 4k reads, while having 90% 4k writes and 10%
8k writes, you would specify:
bssplit=2k/50:4k/50,4k/90:8k/10
Fio supports defining up to 64 different weights for each data direction.
blocksize_unaligned, bs_unaligned
If set, fio will issue I/O units with any size within blocksize_range, not just multiples of the
minimum size. This typically won't work with direct I/O, as that normally requires sector
alignment.
bs_is_seq_rand=bool
If this option is set, fio will use the normal read,write blocksize settings as sequential,random
blocksize settings instead. Any random read or write will use the WRITE blocksize settings, and
any sequential read or write will use the READ blocksize settings.
blockalign=int[,int][,int], ba=int[,int][,int]
Boundary to which fio will align random I/O units. Default: blocksize. Minimum alignment is
typically 512b for using direct I/O, though it usually depends on the hardware block size. This
option is mutually exclusive with using a random map for files, so it will turn off that option.
Comma-separated values may be specified for reads, writes, and trims as described in blocksize.
Buffers and memory
zero_buffers
Initialize buffers with all zeros. Default: fill buffers with random data.
refill_buffers
If this option is given, fio will refill the I/O buffers on every submit. The default is to only
fill it at init time and reuse that data. Only makes sense if zero_buffers isn't specified,
naturally. If data verification is enabled, refill_buffers is also automatically enabled.
scramble_buffers=bool
If refill_buffers is too costly and the target is using data deduplication, then setting this
option will slightly modify the I/O buffer contents to defeat normal de-dupe attempts. This is not
enough to defeat more clever block compression attempts, but it will stop naive dedupe of blocks.
Default: true.
buffer_compress_percentage=int
If this is set, then fio will attempt to provide I/O buffer content (on WRITEs) that compresses to
the specified level. Fio does this by providing a mix of random data followed by fixed pattern
data. The fixed pattern is either zeros, or the pattern specified by buffer_pattern. If the
buffer_pattern option is used, it might skew the compression ratio slightly. Setting
buffer_compress_percentage to a value other than 100 will also enable refill_buffers in order to
reduce the likelihood that adjacent blocks are so similar that they over compress when seen
together. See buffer_compress_chunk for how to set a finer or coarser granularity of the
random/fixed data regions. Defaults to unset i.e., buffer data will not adhere to any compression
level.
buffer_compress_chunk=int
This setting allows fio to manage how big the random/fixed data region is when using
buffer_compress_percentage. When buffer_compress_chunk is set to some non-zero value smaller than
the block size, fio can repeat the random/fixed region throughout the I/O buffer at the specified
interval (which particularly useful when bigger block sizes are used for a job). When set to 0,
fio will use a chunk size that matches the block size resulting in a single random/fixed region
within the I/O buffer. Defaults to 512. When the unit is omitted, the value is interpreted in
bytes.
buffer_pattern=str
If set, fio will fill the I/O buffers with this pattern or with the contents of a file. If not
set, the contents of I/O buffers are defined by the other options related to buffer contents. The
setting can be any pattern of bytes, and can be prefixed with 0x for hex values. It may also be a
string, where the string must then be wrapped with "". Or it may also be a filename, where the
filename must be wrapped with '' in which case the file is opened and read. Note that not all the
file contents will be read if that would cause the buffers to overflow. So, for example:
buffer_pattern='filename'
or:
buffer_pattern="abcd"
or:
buffer_pattern=-12
or:
buffer_pattern=0xdeadface
Also you can combine everything together in any order:
buffer_pattern=0xdeadface"abcd"-12'filename'
dedupe_percentage=int
If set, fio will generate this percentage of identical buffers when writing. These buffers will be
naturally dedupable. The contents of the buffers depend on what other buffer compression settings
have been set. It's possible to have the individual buffers either fully compressible, or not at
all -- this option only controls the distribution of unique buffers. Setting this option will also
enable refill_buffers to prevent every buffer being identical.
dedupe_mode=str
If dedupe_percentage is given, then this option controls how fio generates the dedupe buffers.
repeat
Generate dedupe buffers by repeating previous writes
working_set
Generate dedupe buffers from working set
repeat is the default option for fio. Dedupe buffers are generated by repeating previous unique
write.
working_set is a more realistic workload. With working_set, dedupe_working_set_percentage should
be provided. Given that, fio will use the initial unique write buffers as its working set. Upon
deciding to dedupe, fio will randomly choose a buffer from the working set. Note that by using
working_set the dedupe percentage will converge to the desired over time while repeat maintains
the desired percentage throughout the job.
dedupe_working_set_percentage=int
If dedupe_mode is set to working_set, then this controls the percentage of size of the file or
device used as the buffers fio will choose to generate the dedupe buffers from
Note that size needs to be explicitly provided and only 1 file per job is supported
invalidate=bool
Invalidate the buffer/page cache parts of the files to be used prior to starting I/O if the
platform and file type support it. Defaults to true. This will be ignored if pre_read is also
specified for the same job.
sync=str
Whether, and what type, of synchronous I/O to use for writes. The allowed values are:
none Do not use synchronous IO, the default.
0 Same as none.
sync Use synchronous file IO. For the majority of I/O engines, this means using O_SYNC.
1 Same as sync.
dsync Use synchronous data IO. For the majority of I/O engines, this means using O_DSYNC.
iomem=str, mem=str
Fio can use various types of memory as the I/O unit buffer. The allowed values are:
malloc Use memory from malloc(3) as the buffers. Default memory type.
shm Use shared memory as the buffers. Allocated through shmget(2).
shmhuge
Same as shm, but use huge pages as backing.
mmap Use mmap(2) to allocate buffers. May either be anonymous memory, or can be file
backed if a filename is given after the option. The format is
`mem=mmap:/path/to/file'.
mmaphuge
Use a memory mapped huge file as the buffer backing. Append filename after mmaphuge,
ala `mem=mmaphuge:/hugetlbfs/file'.
mmapshared
Same as mmap, but use a MMAP_SHARED mapping.
cudamalloc
Use GPU memory as the buffers for GPUDirect RDMA benchmark. The ioengine must be
rdma.
The area allocated is a function of the maximum allowed bs size for the job, multiplied by the I/O
depth given. Note that for shmhuge and mmaphuge to work, the system must have free huge pages
allocated. This can normally be checked and set by reading/writing `/proc/sys/vm/nr_hugepages' on
a Linux system. Fio assumes a huge page is 4MiB in size. So to calculate the number of huge pages
you need for a given job file, add up the I/O depth of all jobs (normally one unless iodepth is
used) and multiply by the maximum bs set. Then divide that number by the huge page size. You can
see the size of the huge pages in `/proc/meminfo'. If no huge pages are allocated by having a non-
zero number in `nr_hugepages', using mmaphuge or shmhuge will fail. Also see hugepage-size.
mmaphuge also needs to have hugetlbfs mounted and the file location should point there. So if it's
mounted in `/huge', you would use `mem=mmaphuge:/huge/somefile'.
iomem_align=int, mem_align=int
This indicates the memory alignment of the I/O memory buffers. Note that the given alignment is
applied to the first I/O unit buffer, if using iodepth the alignment of the following buffers are
given by the bs used. In other words, if using a bs that is a multiple of the page sized in the
system, all buffers will be aligned to this value. If using a bs that is not page aligned, the
alignment of subsequent I/O memory buffers is the sum of the iomem_align and bs used.
hugepage-size=int
Defines the size of a huge page. Must at least be equal to the system setting, see
`/proc/meminfo'. Defaults to 4MiB. Should probably always be a multiple of megabytes, so using
`hugepage-size=Xm' is the preferred way to set this to avoid setting a non-pow-2 bad value.
lockmem=int
Pin the specified amount of memory with mlock(2). Can be used to simulate a smaller amount of
memory. The amount specified is per worker.
I/O size
size=int[%|z]
The total size of file I/O for each thread of this job. Fio will run until this many bytes has
been transferred, unless runtime is limited by other options (such as runtime, for instance, or
increased/decreased by io_size). Fio will divide this size between the available files determined
by options such as nrfiles, filename, unless filesize is specified by the job. If the result of
division happens to be 0, the size is set to the physical size of the given files or devices if
they exist. If this option is not specified, fio will use the full size of the given files or
devices. If the files do not exist, size must be given. It is also possible to give size as a
percentage between 1 and 100. If `size=20%' is given, fio will use 20% of the full size of the
given files or devices. In ZBD mode, size can be given in units of number of zones using 'z'. Can
be combined with offset to constrain the start and end range that I/O will be done within.
io_size=int[%|z], io_limit=int[%|z]
Normally fio operates within the region set by size, which means that the size option sets both
the region and size of I/O to be performed. Sometimes that is not what you want. With this option,
it is possible to define just the amount of I/O that fio should do. For instance, if size is set
to 20GiB and io_size is set to 5GiB, fio will perform I/O within the first 20GiB but exit when
5GiB have been done. The opposite is also possible -- if size is set to 20GiB, and io_size is set
to 40GiB, then fio will do 40GiB of I/O within the 0..20GiB region. Value can be set as
percentage: io_size=N%. In this case io_size multiplies size= value. In ZBD mode, value can also
be set as number of zones using 'z'.
filesize=irange(int)
Individual file sizes. May be a range, in which case fio will select sizes for files at random
within the given range and limited to size in total (if that is given). If not given, each created
file is the same size. This option overrides size in terms of file size, which means this value
is used as a fixed size or possible range of each file.
file_append=bool
Perform I/O after the end of the file. Normally fio will operate within the size of a file. If
this option is set, then fio will append to the file instead. This has identical behavior to
setting offset to the size of a file. This option is ignored on non-regular files.
fill_device=bool, fill_fs=bool
Sets size to something really large and waits for ENOSPC (no space left on device) or EDQUOT (disk
quota exceeded) as the terminating condition. Only makes sense with sequential write. For a read
workload, the mount point will be filled first then I/O started on the result.
I/O engine
ioengine=str
Defines how the job issues I/O to the file. The following types are defined:
sync Basic read(2) or write(2) I/O. lseek(2) is used to position the I/O location. See
fsync and fdatasync for syncing write I/Os.
psync Basic pread(2) or pwrite(2) I/O. Default on all supported operating systems except
for Windows.
vsync Basic readv(2) or writev(2) I/O. Will emulate queuing by coalescing adjacent I/Os
into a single submission.
pvsync Basic preadv(2) or pwritev(2) I/O.
pvsync2
Basic preadv2(2) or pwritev2(2) I/O.
libaio Linux native asynchronous I/O. Note that Linux may only support queued behavior with
non-buffered I/O (set `direct=1' or `buffered=0'). This engine defines engine
specific options.
posixaio
POSIX asynchronous I/O using aio_read(3) and aio_write(3).
solarisaio
Solaris native asynchronous I/O.
windowsaio
Windows native asynchronous I/O. Default on Windows.
mmap File is memory mapped with mmap(2) and data copied to/from using memcpy(3).
splice splice(2) is used to transfer the data and vmsplice(2) to transfer data from user
space to the kernel.
sg SCSI generic sg v3 I/O. May either be synchronous using the SG_IO ioctl, or if the
target is an sg character device we use read(2) and write(2) for asynchronous I/O.
Requires filename option to specify either block or character devices. This engine
supports trim operations. The sg engine includes engine specific options.
libzbc Read, write, trim and ZBC/ZAC operations to a zoned block device using libzbc
library. The target can be either an SG character device or a block device file.
null Doesn't transfer any data, just pretends to. This is mainly used to exercise fio
itself and for debugging/testing purposes.
net Transfer over the network to given `host:port'. Depending on the protocol used, the
hostname, port, listen and filename options are used to specify what sort of
connection to make, while the protocol option determines which protocol will be
used. This engine defines engine specific options.
netsplice
Like net, but uses splice(2) and vmsplice(2) to map data and send/receive. This
engine defines engine specific options.
cpuio Doesn't transfer any data, but burns CPU cycles according to the cpuload, cpuchunks
and cpumode options. A job never finishes unless there is at least one non-cpuio
job.
cpuload=85 will cause that job to do nothing but burn 85% of the CPU. In case of
SMP machines, use numjobs=<nr_of_cpu> to get desired CPU usage, as the cpuload only
loads a single CPU at the desired rate.
cpumode=qsort replace the default noop instructions loop by a qsort algorithm to
consume more energy.
rdma The RDMA I/O engine supports both RDMA memory semantics (RDMA_WRITE/RDMA_READ) and
channel semantics (Send/Recv) for the InfiniBand, RoCE and iWARP protocols. This
engine defines engine specific options.
falloc I/O engine that does regular fallocate to simulate data transfer as fio ioengine.
DDIR_READ does fallocate(,mode = FALLOC_FL_KEEP_SIZE,).
DIR_WRITE does fallocate(,mode = 0).
DDIR_TRIM does fallocate(,mode = FALLOC_FL_KEEP_SIZE|FALLOC_FL_PUNCH_HOLE).
ftruncate
I/O engine that sends ftruncate(2) operations in response to write (DDIR_WRITE)
events. Each ftruncate issued sets the file's size to the current block offset.
blocksize is ignored.
e4defrag
I/O engine that does regular EXT4_IOC_MOVE_EXT ioctls to simulate defragment
activity in request to DDIR_WRITE event.
rados I/O engine supporting direct access to Ceph Reliable Autonomic Distributed Object
Store (RADOS) via librados. This ioengine defines engine specific options.
rbd I/O engine supporting direct access to Ceph Rados Block Devices (RBD) via librbd
without the need to use the kernel rbd driver. This ioengine defines engine specific
options.
http I/O engine supporting GET/PUT requests over HTTP(S) with libcurl to a WebDAV or S3
endpoint. This ioengine defines engine specific options.
This engine only supports direct IO of iodepth=1; you need to scale this via
numjobs. blocksize defines the size of the objects to be created.
TRIM is translated to object deletion.
gfapi Using GlusterFS libgfapi sync interface to direct access to GlusterFS volumes
without having to go through FUSE. This ioengine defines engine specific options.
gfapi_async
Using GlusterFS libgfapi async interface to direct access to GlusterFS volumes
without having to go through FUSE. This ioengine defines engine specific options.
libhdfs
Read and write through Hadoop (HDFS). The filename option is used to specify
host,port of the hdfs name-node to connect. This engine interprets offsets a little
differently. In HDFS, files once created cannot be modified so random writes are not
possible. To imitate this the libhdfs engine expects a bunch of small files to be
created over HDFS and will randomly pick a file from them based on the offset
generated by fio backend (see the example job file to create such files, use
`rw=write' option). Please note, it may be necessary to set environment variables to
work with HDFS/libhdfs properly. Each job uses its own connection to HDFS.
mtd Read, write and erase an MTD character device (e.g., `/dev/mtd0'). Discards are
treated as erases. Depending on the underlying device type, the I/O may have to go
in a certain pattern, e.g., on NAND, writing sequentially to erase blocks and
discarding before overwriting. The trimwrite mode works well for this constraint.
pmemblk
Read and write using filesystem DAX to a file on a filesystem mounted with DAX on a
persistent memory device through the PMDK libpmemblk library.
dev-dax
Read and write using device DAX to a persistent memory device (e.g., /dev/dax0.0)
through the PMDK libpmem library.
external
Prefix to specify loading an external I/O engine object file. Append the engine
filename, e.g. `ioengine=external:/tmp/foo.o' to load ioengine `foo.o' in `/tmp'.
The path can be either absolute or relative. See `engines/skeleton_external.c' in
the fio source for details of writing an external I/O engine.
filecreate
Simply create the files and do no I/O to them. You still need to set filesize so
that all the accounting still occurs, but no actual I/O will be done other than
creating the file.
filestat
Simply do stat() and do no I/O to the file. You need to set 'filesize' and
'nrfiles', so that files will be created. This engine is to measure file lookup and
meta data access.
filedelete
Simply delete files by unlink() and do no I/O to the file. You need to set
'filesize' and 'nrfiles', so that files will be created. This engine is to measure
file delete.
libpmem
Read and write using mmap I/O to a file on a filesystem mounted with DAX on a
persistent memory device through the PMDK libpmem library.
ime_psync
Synchronous read and write using DDN's Infinite Memory Engine (IME). This engine is
very basic and issues calls to IME whenever an IO is queued.
ime_psyncv
Synchronous read and write using DDN's Infinite Memory Engine (IME). This engine
uses iovecs and will try to stack as much IOs as possible (if the IOs are
"contiguous" and the IO depth is not exceeded) before issuing a call to IME.
ime_aio
Asynchronous read and write using DDN's Infinite Memory Engine (IME). This engine
will try to stack as much IOs as possible by creating requests for IME. FIO will
then decide when to commit these requests.
libiscsi
Read and write iscsi lun with libiscsi.
nbd Synchronous read and write a Network Block Device (NBD).
libcufile
I/O engine supporting libcufile synchronous access to nvidia-fs and a GPUDirect
Storage-supported filesystem. This engine performs I/O without transferring buffers
between user-space and the kernel, unless verify is set or cuda_io is posix. iomem
must not be cudamalloc. This ioengine defines engine specific options.
dfs I/O engine supporting asynchronous read and write operations to the DAOS File System
(DFS) via libdfs.
nfs I/O engine supporting asynchronous read and write operations to NFS filesystems from
userspace via libnfs. This is useful for achieving higher concurrency and thus
throughput than is possible via kernel NFS.
exec Execute 3rd party tools. Could be used to perform monitoring during jobs runtime.
I/O engine specific parameters
In addition, there are some parameters which are only valid when a specific ioengine is in use. These are
used identically to normal parameters, with the caveat that when used on the command line, they must come
after the ioengine that defines them is selected.
(io_uring,libaio)cmdprio_percentage=int[,int]
Set the percentage of I/O that will be issued with the highest priority. Default: 0. A single
value applies to reads and writes. Comma-separated values may be specified for reads and writes.
This option cannot be used with the `prio` or `prioclass` options. For this option to be
effective, NCQ priority must be supported and enabled, and `direct=1' option must be used. fio
must also be run as the root user.
(io_uring,libaio)cmdprio_class=int[,int]
Set the I/O priority class to use for I/Os that must be issued with a priority when
cmdprio_percentage or cmdprio_bssplit is set. If not specified when cmdprio_percentage or
cmdprio_bssplit is set, this defaults to the highest priority class. A single value applies to
reads and writes. Comma-separated values may be specified for reads and writes. See man ionice(1).
See also the prioclass option.
(io_uring,libaio)cmdprio=int[,int]
Set the I/O priority value to use for I/Os that must be issued with a priority when
cmdprio_percentage or cmdprio_bssplit is set. If not specified when cmdprio_percentage or
cmdprio_bssplit is set, this defaults to 0. Linux limits us to a positive value between 0 and 7,
with 0 being the highest. A single value applies to reads and writes. Comma-separated values may
be specified for reads and writes. See man ionice(1). Refer to an appropriate manpage for other
operating systems since the meaning of priority may differ. See also the prio option.
(io_uring,libaio)cmdprio_bssplit=str[,str]
To get a finer control over I/O priority, this option allows specifying the percentage of IOs that
must have a priority set depending on the block size of the IO. This option is useful only when
used together with the option bssplit, that is, multiple different block sizes are used for reads
and writes. The format for this option is the same as the format of the bssplit option, with the
exception that values for trim IOs are ignored. This option is mutually exclusive with the
cmdprio_percentage option.
(io_uring)fixedbufs
If fio is asked to do direct IO, then Linux will map pages for each IO call, and release them when
IO is done. If this option is set, the pages are pre-mapped before IO is started. This eliminates
the need to map and release for each IO. This is more efficient, and reduces the IO latency as
well.
(io_uring)hipri
If this option is set, fio will attempt to use polled IO completions. Normal IO completions
generate interrupts to signal the completion of IO, polled completions do not. Hence they are
require active reaping by the application. The benefits are more efficient IO for high IOPS
scenarios, and lower latencies for low queue depth IO.
(io_uring)registerfiles
With this option, fio registers the set of files being used with the kernel. This avoids the
overhead of managing file counts in the kernel, making the submission and completion part more
lightweight. Required for the below sqthread_poll option.
(io_uring)sqthread_poll
Normally fio will submit IO by issuing a system call to notify the kernel of available items in
the SQ ring. If this option is set, the act of submitting IO will be done by a polling thread in
the kernel. This frees up cycles for fio, at the cost of using more CPU in the system.
(io_uring)sqthread_poll_cpu
When `sqthread_poll` is set, this option provides a way to define which CPU should be used for the
polling thread.
(libaio)userspace_reap
Normally, with the libaio engine in use, fio will use the io_getevents(3) system call to reap
newly returned events. With this flag turned on, the AIO ring will be read directly from user-
space to reap events. The reaping mode is only enabled when polling for a minimum of 0 events
(e.g. when `iodepth_batch_complete=0').
(pvsync2)hipri
Set RWF_HIPRI on I/O, indicating to the kernel that it's of higher priority than normal.
(pvsync2)hipri_percentage
When hipri is set this determines the probability of a pvsync2 I/O being high priority. The
default is 100%.
(pvsync2,libaio,io_uring)nowait
By default if a request cannot be executed immediately (e.g. resource starvation, waiting on
locks) it is queued and the initiating process will be blocked until the required resource becomes
free. This option sets the RWF_NOWAIT flag (supported from the 4.14 Linux kernel) and the call
will return instantly with EAGAIN or a partial result rather than waiting.
It is useful to also use ignore_error=EAGAIN when using this option. Note: glibc 2.27, 2.28 have
a bug in syscall wrappers preadv2, pwritev2. They return EOPNOTSUP instead of EAGAIN.
For cached I/O, using this option usually means a request operates only with cached data.
Currently the RWF_NOWAIT flag does not supported for cached write. For direct I/O, requests will
only succeed if cache invalidation isn't required, file blocks are fully allocated and the disk
request could be issued immediately.
(cpuio)cpuload=int
Attempt to use the specified percentage of CPU cycles. This is a mandatory option when using cpuio
I/O engine.
(cpuio)cpuchunks=int
Split the load into cycles of the given time. In microseconds.
(cpuio)exit_on_io_done=bool
Detect when I/O threads are done, then exit.
(libhdfs)namenode=str
The hostname or IP address of a HDFS cluster namenode to contact.
(libhdfs)port=int
The listening port of the HFDS cluster namenode.
(netsplice,net)port=int
The TCP or UDP port to bind to or connect to. If this is used with numjobs to spawn multiple
instances of the same job type, then this will be the starting port number since fio will use a
range of ports.
(rdma,librpma_*)port=int
The port to use for RDMA-CM communication. This should be the same value on the client and the
server side.
(netsplice,net,rdma)hostname=str
The hostname or IP address to use for TCP, UDP or RDMA-CM based I/O. If the job is a TCP listener
or UDP reader, the hostname is not used and must be omitted unless it is a valid UDP multicast
address.
(librpma_*)serverip=str
The IP address to be used for RDMA-CM based I/O.
(librpma_*_server)direct_write_to_pmem=bool
Set to 1 only when Direct Write to PMem from the remote host is possible. Otherwise, set to 0.
(librpma_*_server)busy_wait_polling=bool
Set to 0 to wait for completion instead of busy-wait polling completion. Default: 1.
(netsplice,net)interface=str
The IP address of the network interface used to send or receive UDP multicast.
(netsplice,net)ttl=int
Time-to-live value for outgoing UDP multicast packets. Default: 1.
(netsplice,net)nodelay=bool
Set TCP_NODELAY on TCP connections.
(netsplice,net)protocol=str, proto=str
The network protocol to use. Accepted values are:
tcp Transmission control protocol.
tcpv6 Transmission control protocol V6.
udp User datagram protocol.
udpv6 User datagram protocol V6.
unix UNIX domain socket.
When the protocol is TCP or UDP, the port must also be given, as well as the hostname if the job
is a TCP listener or UDP reader. For unix sockets, the normal filename option should be used and
the port is invalid.
(netsplice,net)listen
For TCP network connections, tell fio to listen for incoming connections rather than initiating an
outgoing connection. The hostname must be omitted if this option is used.
(netsplice,net)pingpong
Normally a network writer will just continue writing data, and a network reader will just consume
packages. If `pingpong=1' is set, a writer will send its normal payload to the reader, then wait
for the reader to send the same payload back. This allows fio to measure network latencies. The
submission and completion latencies then measure local time spent sending or receiving, and the
completion latency measures how long it took for the other end to receive and send back. For UDP
multicast traffic `pingpong=1' should only be set for a single reader when multiple readers are
listening to the same address.
(netsplice,net)window_size=int
Set the desired socket buffer size for the connection.
(netsplice,net)mss=int
Set the TCP maximum segment size (TCP_MAXSEG).
(e4defrag)donorname=str
File will be used as a block donor (swap extents between files).
(e4defrag)inplace=int
Configure donor file blocks allocation strategy:
0 Default. Preallocate donor's file on init.
1 Allocate space immediately inside defragment event, and free right after event.
(rbd,rados)clustername=str
Specifies the name of the Ceph cluster.
(rbd)rbdname=str
Specifies the name of the RBD.
(rbd,rados)pool=str
Specifies the name of the Ceph pool containing RBD or RADOS data.
(rbd,rados)clientname=str
Specifies the username (without the 'client.' prefix) used to access the Ceph cluster. If the
clustername is specified, the clientname shall be the full *type.id* string. If no type. prefix is
given, fio will add 'client.' by default.
(rbd,rados)busy_poll=bool
Poll store instead of waiting for completion. Usually this provides better throughput at cost of
higher(up to 100%) CPU utilization.
(rados)touch_objects=bool
During initialization, touch (create if do not exist) all objects (files). Touching all objects
affects ceph caches and likely impacts test results. Enabled by default.
(http)http_host=str
Hostname to connect to. For S3, this could be the bucket name. Default is localhost
(http)http_user=str
Username for HTTP authentication.
(http)http_pass=str
Password for HTTP authentication.
(http)https=str
Whether to use HTTPS instead of plain HTTP. on enables HTTPS; insecure will enable HTTPS, but
disable SSL peer verification (use with caution!). Default is off.
(http)http_mode=str
Which HTTP access mode to use: webdav, swift, or s3. Default is webdav.
(http)http_s3_region=str
The S3 region/zone to include in the request. Default is us-east-1.
(http)http_s3_key=str
The S3 secret key.
(http)http_s3_keyid=str
The S3 key/access id.
(http)http_swift_auth_token=str
The Swift auth token. See the example configuration file on how to retrieve this.
(http)http_verbose=int
Enable verbose requests from libcurl. Useful for debugging. 1 turns on verbose logging from
libcurl, 2 additionally enables HTTP IO tracing. Default is 0
(mtd)skip_bad=bool
Skip operations against known bad blocks.
(libhdfs)hdfsdirectory
libhdfs will create chunk in this HDFS directory.
(libhdfs)chunk_size
The size of the chunk to use for each file.
(rdma)verb=str
The RDMA verb to use on this side of the RDMA ioengine connection. Valid values are write, read,
send and recv. These correspond to the equivalent RDMA verbs (e.g. write = rdma_write etc.). Note
that this only needs to be specified on the client side of the connection. See the examples
folder.
(rdma)bindname=str
The name to use to bind the local RDMA-CM connection to a local RDMA device. This could be a
hostname or an IPv4 or IPv6 address. On the server side this will be passed into the
rdma_bind_addr() function and on the client site it will be used in the rdma_resolve_add()
function. This can be useful when multiple paths exist between the client and the server or in
certain loopback configurations.
(filestat)stat_type=str
Specify stat system call type to measure lookup/getattr performance. Default is stat for stat(2).
(sg)hipri
If this option is set, fio will attempt to use polled IO completions. This will have a similar
effect as (io_uring)hipri. Only SCSI READ and WRITE commands will have the SGV4_FLAG_HIPRI set
(not UNMAP (trim) nor VERIFY). Older versions of the Linux sg driver that do not support hipri
will simply ignore this flag and do normal IO. The Linux SCSI Low Level Driver (LLD) that "owns"
the device also needs to support hipri (also known as iopoll and mq_poll). The MegaRAID driver is
an example of a SCSI LLD. Default: clear (0) which does normal (interrupted based) IO.
(sg)readfua=bool
With readfua option set to 1, read operations include the force unit access (fua) flag. Default:
0.
(sg)writefua=bool
With writefua option set to 1, write operations include the force unit access (fua) flag. Default:
0.
(sg)sg_write_mode=str
Specify the type of write commands to issue. This option can take three values:
write (default)
Write opcodes are issued as usual
verify Issue WRITE AND VERIFY commands. The BYTCHK bit is set to 0. This directs the device
to carry out a medium verification with no data comparison. The writefua option is
ignored with this selection.
same Issue WRITE SAME commands. This transfers a single block to the device and writes
this same block of data to a contiguous sequence of LBAs beginning at the specified
offset. fio's block size parameter specifies the amount of data written with each
command. However, the amount of data actually transferred to the device is equal to
the device's block (sector) size. For a device with 512 byte sectors, blocksize=8k
will write 16 sectors with each command. fio will still generate 8k of data for each
command butonly the first 512 bytes will be used and transferred to the device. The
writefua option is ignored with this selection.
(nbd)uri=str
Specify the NBD URI of the server to test. The string is a standard NBD URI (see
https://github.com/NetworkBlockDevice/nbd/tree/master/doc). Example URIs:
nbd://localhost:10809
nbd+unix:///?socket=/tmp/socket
nbds://tlshost/exportname
(libcufile)gpu_dev_ids=str
Specify the GPU IDs to use with CUDA. This is a colon-separated list of int. GPUs are assigned to
workers roundrobin. Default is 0.
(libcufile)cuda_io=str
Specify the type of I/O to use with CUDA. This option takes the following values:
cufile (default)
Use libcufile and nvidia-fs. This option performs I/O directly between a GPUDirect
Storage filesystem and GPU buffers, avoiding use of a bounce buffer. If verify is
set, cudaMemcpy is used to copy verification data between RAM and GPU(s).
Verification data is copied from RAM to GPU before a write and from GPU to RAM after
a read. direct must be 1.
posix Use POSIX to perform I/O with a RAM buffer, and use cudaMemcpy to transfer data
between RAM and the GPU(s). Data is copied from GPU to RAM before a write and
copied from RAM to GPU after a read. verify does not affect the use of cudaMemcpy.
(dfs)pool
Specify the label or UUID of the DAOS pool to connect to.
(dfs)cont
Specify the label or UUID of the DAOS container to open.
(dfs)chunk_size
Specificy a different chunk size (in bytes) for the dfs file. Use DAOS container's chunk size by
default.
(dfs)object_class
Specificy a different object class for the dfs file. Use DAOS container's object class by
default.
(nfs)nfs_url
URL in libnfs format, eg nfs://<server|ipv4|ipv6>/path[?arg=val[&arg=val]*] Refer to the libnfs
README for more details.
(exec)program=str
Specify the program to execute. Note the program will receive a SIGTERM when the job is reaching
the time limit. A SIGKILL is sent once the job is over. The delay between the two signals is
defined by grace_time option.
(exec)arguments=str
Specify arguments to pass to program. Some special variables can be expanded to pass fio's job
details to the program :
%r replaced by the duration of the job in seconds
%n replaced by the name of the job
(exec)grace_time=int
Defines the time between the SIGTERM and SIGKILL signals. Default is 1 second.
(exec)std_redirect=ool
If set, stdout and stderr streams are redirected to files named from the job name. Default is
true.
I/O depth
iodepth=int
Number of I/O units to keep in flight against the file. Note that increasing iodepth beyond 1 will
not affect synchronous ioengines (except for small degrees when verify_async is in use). Even
async engines may impose OS restrictions causing the desired depth not to be achieved. This may
happen on Linux when using libaio and not setting `direct=1', since buffered I/O is not async on
that OS. Keep an eye on the I/O depth distribution in the fio output to verify that the achieved
depth is as expected. Default: 1.
iodepth_batch_submit=int, iodepth_batch=int
This defines how many pieces of I/O to submit at once. It defaults to 1 which means that we submit
each I/O as soon as it is available, but can be raised to submit bigger batches of I/O at the
time. If it is set to 0 the iodepth value will be used.
iodepth_batch_complete_min=int, iodepth_batch_complete=int
This defines how many pieces of I/O to retrieve at once. It defaults to 1 which means that we'll
ask for a minimum of 1 I/O in the retrieval process from the kernel. The I/O retrieval will go on
until we hit the limit set by iodepth_low. If this variable is set to 0, then fio will always
check for completed events before queuing more I/O. This helps reduce I/O latency, at the cost of
more retrieval system calls.
iodepth_batch_complete_max=int
This defines maximum pieces of I/O to retrieve at once. This variable should be used along with
iodepth_batch_complete_min=int variable, specifying the range of min and max amount of I/O which
should be retrieved. By default it is equal to iodepth_batch_complete_min value. Example #1:
iodepth_batch_complete_min=1
iodepth_batch_complete_max=<iodepth>
which means that we will retrieve at least 1 I/O and up to the whole submitted queue depth. If
none of I/O has been completed yet, we will wait. Example #2:
iodepth_batch_complete_min=0
iodepth_batch_complete_max=<iodepth>
which means that we can retrieve up to the whole submitted queue depth, but if none of I/O has
been completed yet, we will NOT wait and immediately exit the system call. In this example we
simply do polling.
iodepth_low=int
The low water mark indicating when to start filling the queue again. Defaults to the same as
iodepth, meaning that fio will attempt to keep the queue full at all times. If iodepth is set to
e.g. 16 and iodepth_low is set to 4, then after fio has filled the queue of 16 requests, it will
let the depth drain down to 4 before starting to fill it again.
serialize_overlap=bool
Serialize in-flight I/Os that might otherwise cause or suffer from data races. When two or more
I/Os are submitted simultaneously, there is no guarantee that the I/Os will be processed or
completed in the submitted order. Further, if two or more of those I/Os are writes, any
overlapping region between them can become indeterminate/undefined on certain storage. These
issues can cause verification to fail erratically when at least one of the racing I/Os is changing
data and the overlapping region has a non-zero size. Setting serialize_overlap tells fio to avoid
provoking this behavior by explicitly serializing in-flight I/Os that have a non-zero overlap.
Note that setting this option can reduce both performance and the iodepth achieved.
This option only applies to I/Os issued for a single job except when it is enabled along with
io_submit_mode=offload. In offload mode, fio will check for overlap among all I/Os submitted by
offload jobs with serialize_overlap enabled.
Default: false.
io_submit_mode=str
This option controls how fio submits the I/O to the I/O engine. The default is `inline', which
means that the fio job threads submit and reap I/O directly. If set to `offload', the job threads
will offload I/O submission to a dedicated pool of I/O threads. This requires some coordination
and thus has a bit of extra overhead, especially for lower queue depth I/O where it can increase
latencies. The benefit is that fio can manage submission rates independently of the device
completion rates. This avoids skewed latency reporting if I/O gets backed up on the device side
(the coordinated omission problem). Note that this option cannot reliably be used with async IO
engines.
I/O rate
thinktime=time
Stall the job for the specified period of time after an I/O has completed before issuing the next.
May be used to simulate processing being done by an application. When the unit is omitted, the
value is interpreted in microseconds. See thinktime_blocks, thinktime_iotime and thinktime_spin.
thinktime_spin=time
Only valid if thinktime is set - pretend to spend CPU time doing something with the data received,
before falling back to sleeping for the rest of the period specified by thinktime. When the unit
is omitted, the value is interpreted in microseconds.
thinktime_blocks=int
Only valid if thinktime is set - control how many blocks to issue, before waiting thinktime usecs.
If not set, defaults to 1 which will make fio wait thinktime usecs after every block. This
effectively makes any queue depth setting redundant, since no more than 1 I/O will be queued
before we have to complete it and do our thinktime. In other words, this setting effectively caps
the queue depth if the latter is larger.
thinktime_blocks_type=str
Only valid if thinktime is set - control how thinktime_blocks triggers. The default is
`complete', which triggers thinktime when fio completes thinktime_blocks blocks. If this is set to
`issue', then the trigger happens at the issue side.
thinktime_iotime=time
Only valid if thinktime is set - control thinktime interval by time. The thinktime stall is
repeated after IOs are executed for thinktime_iotime. For example, `--thinktime_iotime=9s
--thinktime=1s' repeat 10-second cycle with IOs for 9 seconds and stall for 1 second. When the
unit is omitted, thinktime_iotime is interpreted as a number of seconds. If this option is used
together with thinktime_blocks, the thinktime stall is repeated after thinktime_iotime or after
thinktime_blocks IOs, whichever happens first.
rate=int[,int][,int]
Cap the bandwidth used by this job. The number is in bytes/sec, the normal suffix rules apply.
Comma-separated values may be specified for reads, writes, and trims as described in blocksize.
For example, using `rate=1m,500k' would limit reads to 1MiB/sec and writes to 500KiB/sec. Capping
only reads or writes can be done with `rate=,500k' or `rate=500k,' where the former will only
limit writes (to 500KiB/sec) and the latter will only limit reads.
rate_min=int[,int][,int]
Tell fio to do whatever it can to maintain at least this bandwidth. Failing to meet this
requirement will cause the job to exit. Comma-separated values may be specified for reads, writes,
and trims as described in blocksize.
rate_iops=int[,int][,int]
Cap the bandwidth to this number of IOPS. Basically the same as rate, just specified independently
of bandwidth. If the job is given a block size range instead of a fixed value, the smallest block
size is used as the metric. Comma-separated values may be specified for reads, writes, and trims
as described in blocksize.
rate_iops_min=int[,int][,int]
If fio doesn't meet this rate of I/O, it will cause the job to exit. Comma-separated values may
be specified for reads, writes, and trims as described in blocksize.
rate_process=str
This option controls how fio manages rated I/O submissions. The default is `linear', which submits
I/O in a linear fashion with fixed delays between I/Os that gets adjusted based on I/O completion
rates. If this is set to `poisson', fio will submit I/O based on a more real world random request
flow, known as the Poisson process (https://en.wikipedia.org/wiki/Poisson_point_process). The
lambda will be 10^6 / IOPS for the given workload.
rate_ignore_thinktime=bool
By default, fio will attempt to catch up to the specified rate setting, if any kind of thinktime
setting was used. If this option is set, then fio will ignore the thinktime and continue doing IO
at the specified rate, instead of entering a catch-up mode after thinktime is done.
I/O latency
latency_target=time
If set, fio will attempt to find the max performance point that the given workload will run at
while maintaining a latency below this target. When the unit is omitted, the value is interpreted
in microseconds. See latency_window and latency_percentile.
latency_window=time
Used with latency_target to specify the sample window that the job is run at varying queue depths
to test the performance. When the unit is omitted, the value is interpreted in microseconds.
latency_percentile=float
The percentage of I/Os that must fall within the criteria specified by latency_target and
latency_window. If not set, this defaults to 100.0, meaning that all I/Os must be equal or below
to the value set by latency_target.
latency_run=bool
Used with latency_target. If false (default), fio will find the highest queue depth that meets
latency_target and exit. If true, fio will continue running and try to meet latency_target by
adjusting queue depth.
max_latency=time[,time][,time]
If set, fio will exit the job with an ETIMEDOUT error if it exceeds this maximum latency. When the
unit is omitted, the value is interpreted in microseconds. Comma-separated values may be specified
for reads, writes, and trims as described in blocksize.
rate_cycle=int
Average bandwidth for rate and rate_min over this number of milliseconds. Defaults to 1000.
I/O replay
write_iolog=str
Write the issued I/O patterns to the specified file. See read_iolog. Specify a separate file for
each job, otherwise the iologs will be interspersed and the file may be corrupt.
read_iolog=str
Open an iolog with the specified filename and replay the I/O patterns it contains. This can be
used to store a workload and replay it sometime later. The iolog given may also be a blktrace
binary file, which allows fio to replay a workload captured by blktrace. See blktrace(8) for how
to capture such logging data. For blktrace replay, the file needs to be turned into a blkparse
binary data file first (`blkparse <device> -o /dev/null -d file_for_fio.bin'). You can specify a
number of files by separating the names with a ':' character. See the filename option for
information on how to escape ':' characters within the file names. These files will be
sequentially assigned to job clones created by numjobs. '-' is a reserved name, meaning read from
stdin, notably if filename is set to '-' which means stdin as well, then this flag can't be set to
'-'.
read_iolog_chunked=bool
Determines how iolog is read. If false (default) entire read_iolog will be read at once. If
selected true, input from iolog will be read gradually. Useful when iolog is very large, or it is
generated.
merge_blktrace_file=str
When specified, rather than replaying the logs passed to read_iolog, the logs go through a merge
phase which aggregates them into a single blktrace. The resulting file is then passed on as the
read_iolog parameter. The intention here is to make the order of events consistent. This limits
the influence of the scheduler compared to replaying multiple blktraces via concurrent jobs.
merge_blktrace_scalars=float_list
This is a percentage based option that is index paired with the list of files passed to
read_iolog. When merging is performed, scale the time of each event by the corresponding amount.
For example, `--merge_blktrace_scalars="50:100"' runs the first trace in halftime and the second
trace in realtime. This knob is separately tunable from replay_time_scale which scales the trace
during runtime and will not change the output of the merge unlike this option.
merge_blktrace_iters=float_list
This is a whole number option that is index paired with the list of files passed to read_iolog.
When merging is performed, run each trace for the specified number of iterations. For example,
`--merge_blktrace_iters="2:1"' runs the first trace for two iterations and the second trace for
one iteration.
replay_no_stall=bool
When replaying I/O with read_iolog the default behavior is to attempt to respect the timestamps
within the log and replay them with the appropriate delay between IOPS. By setting this variable
fio will not respect the timestamps and attempt to replay them as fast as possible while still
respecting ordering. The result is the same I/O pattern to a given device, but different timings.
replay_time_scale=int
When replaying I/O with read_iolog, fio will honor the original timing in the trace. With this
option, it's possible to scale the time. It's a percentage option, if set to 50 it means run at
50% the original IO rate in the trace. If set to 200, run at twice the original IO rate. Defaults
to 100.
replay_redirect=str
While replaying I/O patterns using read_iolog the default behavior is to replay the IOPS onto the
major/minor device that each IOP was recorded from. This is sometimes undesirable because on a
different machine those major/minor numbers can map to a different device. Changing hardware on
the same system can also result in a different major/minor mapping. replay_redirect causes all
I/Os to be replayed onto the single specified device regardless of the device it was recorded
from. i.e. `replay_redirect=/dev/sdc' would cause all I/O in the blktrace or iolog to be replayed
onto `/dev/sdc'. This means multiple devices will be replayed onto a single device, if the trace
contains multiple devices. If you want multiple devices to be replayed concurrently to multiple
redirected devices you must blkparse your trace into separate traces and replay them with
independent fio invocations. Unfortunately this also breaks the strict time ordering between
multiple device accesses.
replay_align=int
Force alignment of the byte offsets in a trace to this value. The value must be a power of 2.
replay_scale=int
Scale bye offsets down by this factor when replaying traces. Should most likely use replay_align
as well.
Threads, processes and job synchronization
replay_skip=str
Sometimes it's useful to skip certain IO types in a replay trace. This could be, for instance,
eliminating the writes in the trace. Or not replaying the trims/discards, if you are redirecting
to a device that doesn't support them. This option takes a comma separated list of read, write,
trim, sync.
thread Fio defaults to creating jobs by using fork, however if this option is given, fio will create jobs
by using POSIX Threads' function pthread_create(3) to create threads instead.
wait_for=str
If set, the current job won't be started until all workers of the specified waitee job are done.
wait_for operates on the job name basis, so there are a few limitations. First, the waitee must be
defined prior to the waiter job (meaning no forward references). Second, if a job is being
referenced as a waitee, it must have a unique name (no duplicate waitees).
nice=int
Run the job with the given nice value. See man nice(2). On Windows, values less than -15 set the
process class to "High"; -1 through -15 set "Above Normal"; 1 through 15 "Below Normal"; and above
15 "Idle" priority class.
prio=int
Set the I/O priority value of this job. Linux limits us to a positive value between 0 and 7, with
0 being the highest. See man ionice(1). Refer to an appropriate manpage for other operating
systems since meaning of priority may differ. For per-command priority setting, see the I/O engine
specific `cmdprio_percentage` and `cmdprio` options.
prioclass=int
Set the I/O priority class. See man ionice(1). For per-command priority setting, see the I/O
engine specific `cmdprio_percentage` and `cmdprio_class` options.
cpus_allowed=str
Controls the same options as cpumask, but accepts a textual specification of the permitted CPUs
instead and CPUs are indexed from 0. So to use CPUs 0 and 5 you would specify `cpus_allowed=0,5'.
This option also allows a range of CPUs to be specified -- say you wanted a binding to CPUs 0, 5,
and 8 to 15, you would set `cpus_allowed=0,5,8-15'.
On Windows, when `cpus_allowed' is unset only CPUs from fio's current processor group will be used
and affinity settings are inherited from the system. An fio build configured to target Windows 7
makes options that set CPUs processor group aware and values will set both the processor group and
a CPU from within that group. For example, on a system where processor group 0 has 40 CPUs and
processor group 1 has 32 CPUs, `cpus_allowed' values between 0 and 39 will bind CPUs from
processor group 0 and `cpus_allowed' values between 40 and 71 will bind CPUs from processor group
1. When using `cpus_allowed_policy=shared' all CPUs specified by a single `cpus_allowed' option
must be from the same processor group. For Windows fio builds not built for Windows 7, CPUs will
only be selected from (and be relative to) whatever processor group fio happens to be running in
and CPUs from other processor groups cannot be used.
cpus_allowed_policy=str
Set the policy of how fio distributes the CPUs specified by cpus_allowed or cpumask. Two policies
are supported:
shared All jobs will share the CPU set specified.
split Each job will get a unique CPU from the CPU set.
shared is the default behavior, if the option isn't specified. If split is specified, then fio
will assign one cpu per job. If not enough CPUs are given for the jobs listed, then fio will
roundrobin the CPUs in the set.
cpumask=int
Set the CPU affinity of this job. The parameter given is a bit mask of allowed CPUs the job may
run on. So if you want the allowed CPUs to be 1 and 5, you would pass the decimal value of (1 << 1
| 1 << 5), or 34. See man sched_setaffinity(2). This may not work on all supported operating
systems or kernel versions. This option doesn't work well for a higher CPU count than what you can
store in an integer mask, so it can only control cpus 1-32. For boxes with larger CPU counts, use
cpus_allowed.
numa_cpu_nodes=str
Set this job running on specified NUMA nodes' CPUs. The arguments allow comma delimited list of
cpu numbers, A-B ranges, or `all'. Note, to enable NUMA options support, fio must be built on a
system with libnuma-dev(el) installed.
numa_mem_policy=str
Set this job's memory policy and corresponding NUMA nodes. Format of the arguments:
<mode>[:<nodelist>]
`mode' is one of the following memory policies: `default', `prefer', `bind', `interleave' or
`local'. For `default' and `local' memory policies, no node needs to be specified. For `prefer',
only one node is allowed. For `bind' and `interleave' the `nodelist' may be as follows: a comma
delimited list of numbers, A-B ranges, or `all'.
cgroup=str
Add job to this control group. If it doesn't exist, it will be created. The system must have a
mounted cgroup blkio mount point for this to work. If your system doesn't have it mounted, you can
do so with:
# mount -t cgroup -o blkio none /cgroup
cgroup_weight=int
Set the weight of the cgroup to this value. See the documentation that comes with the kernel,
allowed values are in the range of 100..1000.
cgroup_nodelete=bool
Normally fio will delete the cgroups it has created after the job completion. To override this
behavior and to leave cgroups around after the job completion, set `cgroup_nodelete=1'. This can
be useful if one wants to inspect various cgroup files after job completion. Default: false.
flow_id=int
The ID of the flow. If not specified, it defaults to being a global flow. See flow.
flow=int
Weight in token-based flow control. If this value is used, then fio regulates the activity between
two or more jobs sharing the same flow_id. Fio attempts to keep each job activity proportional to
other jobs' activities in the same flow_id group, with respect to requested weight per job. That
is, if one job has `flow=3', another job has `flow=2' and another with `flow=1`, then there will
be a roughly 3:2:1 ratio in how much one runs vs the others.
flow_sleep=int
The period of time, in microseconds, to wait after the flow counter has exceeded its proportion
before retrying operations.
stonewall, wait_for_previous
Wait for preceding jobs in the job file to exit, before starting this one. Can be used to insert
serialization points in the job file. A stone wall also implies starting a new reporting group,
see group_reporting. Optionally you can use `stonewall=0` to disable or `stonewall=1` to enable
it.
exitall
By default, fio will continue running all other jobs when one job finishes. Sometimes this is not
the desired action. Setting exitall will instead make fio terminate all jobs in the same group, as
soon as one job of that group finishes.
exit_what=str
By default, fio will continue running all other jobs when one job finishes. Sometimes this is not
the desired action. Setting exitall will instead make fio terminate all jobs in the same group.
The option exit_what allows you to control which jobs get terminated when exitall is enabled. The
default value is group. The allowed values are:
all terminates all jobs.
group is the default and does not change the behaviour of exitall.
stonewall
terminates all currently running jobs across all groups and continues execution with
the next stonewalled group.
exec_prerun=str
Before running this job, issue the command specified through system(3). Output is redirected in a
file called `jobname.prerun.txt'.
exec_postrun=str
After the job completes, issue the command specified though system(3). Output is redirected in a
file called `jobname.postrun.txt'.
uid=int
Instead of running as the invoking user, set the user ID to this value before the thread/process
does any work.
gid=int
Set group ID, see uid.
Verification
verify_only
Do not perform specified workload, only verify data still matches previous invocation of this
workload. This option allows one to check data multiple times at a later date without overwriting
it. This option makes sense only for workloads that write data, and does not support workloads
with the time_based option set.
do_verify=bool
Run the verify phase after a write phase. Only valid if verify is set. Default: true.
verify=str
If writing to a file, fio can verify the file contents after each iteration of the job. Each
verification method also implies verification of special header, which is written to the beginning
of each block. This header also includes meta information, like offset of the block, block number,
timestamp when block was written, etc. verify can be combined with verify_pattern option. The
allowed values are:
md5 Use an md5 sum of the data area and store it in the header of each block.
crc64 Use an experimental crc64 sum of the data area and store it in the header of each
block.
crc32c Use a crc32c sum of the data area and store it in the header of each block. This
will automatically use hardware acceleration (e.g. SSE4.2 on an x86 or CRC crypto
extensions on ARM64) but will fall back to software crc32c if none is found.
Generally the fastest checksum fio supports when hardware accelerated.
crc32c-intel
Synonym for crc32c.
crc32 Use a crc32 sum of the data area and store it in the header of each block.
crc16 Use a crc16 sum of the data area and store it in the header of each block.
crc7 Use a crc7 sum of the data area and store it in the header of each block.
xxhash Use xxhash as the checksum function. Generally the fastest software checksum that
fio supports.
sha512 Use sha512 as the checksum function.
sha256 Use sha256 as the checksum function.
sha1 Use optimized sha1 as the checksum function.
sha3-224
Use optimized sha3-224 as the checksum function.
sha3-256
Use optimized sha3-256 as the checksum function.
sha3-384
Use optimized sha3-384 as the checksum function.
sha3-512
Use optimized sha3-512 as the checksum function.
meta This option is deprecated, since now meta information is included in generic
verification header and meta verification happens by default. For detailed
information see the description of the verify setting. This option is kept because
of compatibility's sake with old configurations. Do not use it.
pattern
Verify a strict pattern. Normally fio includes a header with some basic information
and checksumming, but if this option is set, only the specific pattern set with
verify_pattern is verified.
null Only pretend to verify. Useful for testing internals with `ioengine=null', not for
much else.
This option can be used for repeated burn-in tests of a system to make sure that the written data
is also correctly read back. If the data direction given is a read or random read, fio will assume
that it should verify a previously written file. If the data direction includes any form of write,
the verify will be of the newly written data.
To avoid false verification errors, do not use the norandommap option when verifying data with
async I/O engines and I/O depths > 1. Or use the norandommap and the lfsr random generator
together to avoid writing to the same offset with muliple outstanding I/Os.
verify_offset=int
Swap the verification header with data somewhere else in the block before writing. It is swapped
back before verifying.
verify_interval=int
Write the verification header at a finer granularity than the blocksize. It will be written for
chunks the size of verify_interval. blocksize should divide this evenly.
verify_pattern=str
If set, fio will fill the I/O buffers with this pattern. Fio defaults to filling with totally
random bytes, but sometimes it's interesting to fill with a known pattern for I/O verification
purposes. Depending on the width of the pattern, fio will fill 1/2/3/4 bytes of the buffer at the
time (it can be either a decimal or a hex number). The verify_pattern if larger than a 32-bit
quantity has to be a hex number that starts with either "0x" or "0X". Use with verify. Also,
verify_pattern supports %o format, which means that for each block offset will be written and then
verified back, e.g.:
verify_pattern=%o
Or use combination of everything:
verify_pattern=0xff%o"abcd"-12
verify_fatal=bool
Normally fio will keep checking the entire contents before quitting on a block verification
failure. If this option is set, fio will exit the job on the first observed failure. Default:
false.
verify_dump=bool
If set, dump the contents of both the original data block and the data block we read off disk to
files. This allows later analysis to inspect just what kind of data corruption occurred. Off by
default.
verify_async=int
Fio will normally verify I/O inline from the submitting thread. This option takes an integer
describing how many async offload threads to create for I/O verification instead, causing fio to
offload the duty of verifying I/O contents to one or more separate threads. If using this offload
option, even sync I/O engines can benefit from using an iodepth setting higher than 1, as it
allows them to have I/O in flight while verifies are running. Defaults to 0 async threads, i.e.
verification is not asynchronous.
verify_async_cpus=str
Tell fio to set the given CPU affinity on the async I/O verification threads. See cpus_allowed for
the format used.
verify_backlog=int
Fio will normally verify the written contents of a job that utilizes verify once that job has
completed. In other words, everything is written then everything is read back and verified. You
may want to verify continually instead for a variety of reasons. Fio stores the meta data
associated with an I/O block in memory, so for large verify workloads, quite a bit of memory would
be used up holding this meta data. If this option is enabled, fio will write only N blocks before
verifying these blocks.
verify_backlog_batch=int
Control how many blocks fio will verify if verify_backlog is set. If not set, will default to the
value of verify_backlog (meaning the entire queue is read back and verified). If
verify_backlog_batch is less than verify_backlog then not all blocks will be verified, if
verify_backlog_batch is larger than verify_backlog, some blocks will be verified more than once.
verify_state_save=bool
When a job exits during the write phase of a verify workload, save its current state. This allows
fio to replay up until that point, if the verify state is loaded for the verify read phase. The
format of the filename is, roughly:
<type>-<jobname>-<jobindex>-verify.state.
<type> is "local" for a local run, "sock" for a client/server socket connection, and "ip"
(192.168.0.1, for instance) for a networked client/server connection. Defaults to true.
verify_state_load=bool
If a verify termination trigger was used, fio stores the current write state of each thread. This
can be used at verification time so that fio knows how far it should verify. Without this
information, fio will run a full verification pass, according to the settings in the job file
used. Default false.
trim_percentage=int
Number of verify blocks to discard/trim.
trim_verify_zero=bool
Verify that trim/discarded blocks are returned as zeros.
trim_backlog=int
Verify that trim/discarded blocks are returned as zeros.
trim_backlog_batch=int
Trim this number of I/O blocks.
experimental_verify=bool
Enable experimental verification.
Steady state
steadystate=str:float, ss=str:float
Define the criterion and limit for assessing steady state performance. The first parameter
designates the criterion whereas the second parameter sets the threshold. When the criterion falls
below the threshold for the specified duration, the job will stop. For example, `iops_slope:0.1%'
will direct fio to terminate the job when the least squares regression slope falls below 0.1% of
the mean IOPS. If group_reporting is enabled this will apply to all jobs in the group. Below is
the list of available steady state assessment criteria. All assessments are carried out using only
data from the rolling collection window. Threshold limits can be expressed as a fixed value or as
a percentage of the mean in the collection window.
When using this feature, most jobs should include the time_based and runtime options or the loops
option so that fio does not stop running after it has covered the full size of the specified
file(s) or device(s).
iops Collect IOPS data. Stop the job if all individual IOPS measurements are
within the specified limit of the mean IOPS (e.g., `iops:2' means that all
individual IOPS values must be within 2 of the mean, whereas `iops:0.2%'
means that all individual IOPS values must be within 0.2% of the mean IOPS to
terminate the job).
iops_slope
Collect IOPS data and calculate the least squares regression slope. Stop the
job if the slope falls below the specified limit.
bw Collect bandwidth data. Stop the job if all individual bandwidth measurements
are within the specified limit of the mean bandwidth.
bw_slope
Collect bandwidth data and calculate the least squares regression slope. Stop
the job if the slope falls below the specified limit.
steadystate_duration=time, ss_dur=time
A rolling window of this duration will be used to judge whether steady state has been
reached. Data will be collected once per second. The default is 0 which disables steady
state detection. When the unit is omitted, the value is interpreted in seconds.
steadystate_ramp_time=time, ss_ramp=time
Allow the job to run for the specified duration before beginning data collection for
checking the steady state job termination criterion. The default is 0. When the unit is
omitted, the value is interpreted in seconds.
Measurements and reporting
per_job_logs=bool
If set, this generates bw/clat/iops log with per file private filenames. If not set, jobs with
identical names will share the log filename. Default: true.
group_reporting
It may sometimes be interesting to display statistics for groups of jobs as a whole instead of for
each individual job. This is especially true if numjobs is used; looking at individual
thread/process output quickly becomes unwieldy. To see the final report per-group instead of per-
job, use group_reporting. Jobs in a file will be part of the same reporting group, unless if
separated by a stonewall, or by using new_group.
new_group
Start a new reporting group. See: group_reporting. If not given, all jobs in a file will be part
of the same reporting group, unless separated by a stonewall.
stats=bool
By default, fio collects and shows final output results for all jobs that run. If this option is
set to 0, then fio will ignore it in the final stat output.
write_bw_log=str
If given, write a bandwidth log for this job. Can be used to store data of the bandwidth of the
jobs in their lifetime.
If no str argument is given, the default filename of `jobname_type.x.log' is used. Even when the
argument is given, fio will still append the type of log. So if one specifies:
write_bw_log=foo
The actual log name will be `foo_bw.x.log' where `x' is the index of the job (1..N, where N is the
number of jobs). If per_job_logs is false, then the filename will not include the `.x` job index.
The included fio_generate_plots script uses gnuplot to turn these text files into nice graphs. See
the LOG FILE FORMATS section for how data is structured within the file.
write_lat_log=str
Same as write_bw_log, except this option creates I/O submission (e.g., `name_slat.x.log'),
completion (e.g., `name_clat.x.log'), and total (e.g., `name_lat.x.log') latency files instead.
See write_bw_log for details about the filename format and the LOG FILE FORMATS section for how
data is structured within the files.
write_hist_log=str
Same as write_bw_log but writes an I/O completion latency histogram file (e.g., `name_hist.x.log')
instead. Note that this file will be empty unless log_hist_msec has also been set. See
write_bw_log for details about the filename format and the LOG FILE FORMATS section for how data
is structured within the file.
write_iops_log=str
Same as write_bw_log, but writes an IOPS file (e.g. `name_iops.x.log`) instead. Because fio
defaults to individual I/O logging, the value entry in the IOPS log will be 1 unless windowed
logging (see log_avg_msec) has been enabled. See write_bw_log for details about the filename
format and LOG FILE FORMATS for how data is structured within the file.
log_avg_msec=int
By default, fio will log an entry in the iops, latency, or bw log for every I/O that completes.
When writing to the disk log, that can quickly grow to a very large size. Setting this option
makes fio average the each log entry over the specified period of time, reducing the resolution of
the log. See log_max_value as well. Defaults to 0, logging all entries. Also see LOG FILE FORMATS
section.
log_hist_msec=int
Same as log_avg_msec, but logs entries for completion latency histograms. Computing latency
percentiles from averages of intervals using log_avg_msec is inaccurate. Setting this option makes
fio log histogram entries over the specified period of time, reducing log sizes for high IOPS
devices while retaining percentile accuracy. See log_hist_coarseness and write_hist_log as well.
Defaults to 0, meaning histogram logging is disabled.
log_hist_coarseness=int
Integer ranging from 0 to 6, defining the coarseness of the resolution of the histogram logs
enabled with log_hist_msec. For each increment in coarseness, fio outputs half as many bins.
Defaults to 0, for which histogram logs contain 1216 latency bins. See LOG FILE FORMATS section.
log_max_value=bool
If log_avg_msec is set, fio logs the average over that window. If you instead want to log the
maximum value, set this option to 1. Defaults to 0, meaning that averaged values are logged.
log_offset=bool
If this is set, the iolog options will include the byte offset for the I/O entry as well as the
other data values. Defaults to 0 meaning that offsets are not present in logs. Also see LOG FILE
FORMATS section.
log_prio=bool
If this is set, the iolog options will include the I/O priority for the I/O entry as well as the
other data values. Defaults to 0 meaning that I/O priorities are not present in logs. Also see LOG
FILE FORMATS section.
log_compression=int
If this is set, fio will compress the I/O logs as it goes, to keep the memory footprint lower.
When a log reaches the specified size, that chunk is removed and compressed in the background.
Given that I/O logs are fairly highly compressible, this yields a nice memory savings for longer
runs. The downside is that the compression will consume some background CPU cycles, so it may
impact the run. This, however, is also true if the logging ends up consuming most of the system
memory. So pick your poison. The I/O logs are saved normally at the end of a run, by decompressing
the chunks and storing them in the specified log file. This feature depends on the availability of
zlib.
log_compression_cpus=str
Define the set of CPUs that are allowed to handle online log compression for the I/O jobs. This
can provide better isolation between performance sensitive jobs, and background compression work.
See cpus_allowed for the format used.
log_store_compressed=bool
If set, fio will store the log files in a compressed format. They can be decompressed with fio,
using the --inflate-log command line parameter. The files will be stored with a `.fz' suffix.
log_unix_epoch=bool
If set, fio will log Unix timestamps to the log files produced by enabling write_type_log for each
log type, instead of the default zero-based timestamps.
block_error_percentiles=bool
If set, record errors in trim block-sized units from writes and trims and output a histogram of
how many trims it took to get to errors, and what kind of error was encountered.
bwavgtime=int
Average the calculated bandwidth over the given time. Value is specified in milliseconds. If the
job also does bandwidth logging through write_bw_log, then the minimum of this option and
log_avg_msec will be used. Default: 500ms.
iopsavgtime=int
Average the calculated IOPS over the given time. Value is specified in milliseconds. If the job
also does IOPS logging through write_iops_log, then the minimum of this option and log_avg_msec
will be used. Default: 500ms.
disk_util=bool
Generate disk utilization statistics, if the platform supports it. Default: true.
disable_lat=bool
Disable measurements of total latency numbers. Useful only for cutting back the number of calls to
gettimeofday(2), as that does impact performance at really high IOPS rates. Note that to really
get rid of a large amount of these calls, this option must be used with disable_slat and
disable_bw_measurement as well.
disable_clat=bool
Disable measurements of completion latency numbers. See disable_lat.
disable_slat=bool
Disable measurements of submission latency numbers. See disable_lat.
disable_bw_measurement=bool, disable_bw=bool
Disable measurements of throughput/bandwidth numbers. See disable_lat.
slat_percentiles=bool
Report submission latency percentiles. Submission latency is not recorded for synchronous
ioengines.
clat_percentiles=bool
Report completion latency percentiles.
lat_percentiles=bool
Report total latency percentiles. Total latency is the sum of submission latency and completion
latency.
percentile_list=float_list
Overwrite the default list of percentiles for latencies and the block error histogram. Each number
is a floating point number in the range (0,100], and the maximum length of the list is 20. Use ':'
to separate the numbers. For example, `--percentile_list=99.5:99.9' will cause fio to report the
latency durations below which 99.5% and 99.9% of the observed latencies fell, respectively.
significant_figures=int
If using --output-format of `normal', set the significant figures to this value. Higher values
will yield more precise IOPS and throughput units, while lower values will round. Requires a
minimum value of 1 and a maximum value of 10. Defaults to 4.
Error handling
exitall_on_error
When one job finishes in error, terminate the rest. The default is to wait for each job to finish.
continue_on_error=str
Normally fio will exit the job on the first observed failure. If this option is set, fio will
continue the job when there is a 'non-fatal error' (EIO or EILSEQ) until the runtime is exceeded
or the I/O size specified is completed. If this option is used, there are two more stats that are
appended, the total error count and the first error. The error field given in the stats is the
first error that was hit during the run. The allowed values are:
none Exit on any I/O or verify errors.
read Continue on read errors, exit on all others.
write Continue on write errors, exit on all others.
io Continue on any I/O error, exit on all others.
verify Continue on verify errors, exit on all others.
all Continue on all errors.
0 Backward-compatible alias for 'none'.
1 Backward-compatible alias for 'all'.
ignore_error=str
Sometimes you want to ignore some errors during test in that case you can specify error list for
each error type, instead of only being able to ignore the default 'non-fatal error' using
continue_on_error. `ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST' errors for given
error type is separated with ':'. Error may be symbol ('ENOSPC', 'ENOMEM') or integer. Example:
ignore_error=EAGAIN,ENOSPC:122
This option will ignore EAGAIN from READ, and ENOSPC and 122(EDQUOT) from WRITE. This option works
by overriding continue_on_error with the list of errors for each error type if any.
error_dump=bool
If set dump every error even if it is non fatal, true by default. If disabled only fatal error
will be dumped.
Running predefined workloads
Fio includes predefined profiles that mimic the I/O workloads generated by other tools.
profile=str
The predefined workload to run. Current profiles are:
tiobench
Threaded I/O bench (tiotest/tiobench) like workload.
act Aerospike Certification Tool (ACT) like workload.
To view a profile's additional options use --cmdhelp after specifying the profile. For example:
$ fio --profile=act --cmdhelp
Act profile options
device-names=str
Devices to use.
load=int
ACT load multiplier. Default: 1.
test-duration=time
How long the entire test takes to run. When the unit is omitted, the value is given in seconds.
Default: 24h.
threads-per-queue=int
Number of read I/O threads per device. Default: 8.
read-req-num-512-blocks=int
Number of 512B blocks to read at the time. Default: 3.
large-block-op-kbytes=int
Size of large block ops in KiB (writes). Default: 131072.
prep Set to run ACT prep phase.
Tiobench profile options
size=str
Size in MiB.
block=int
Block size in bytes. Default: 4096.
numruns=int
Number of runs.
dir=str
Test directory.
threads=int
Number of threads.
OUTPUT
Fio spits out a lot of output. While running, fio will display the status of the jobs created. An example
of that would be:
Jobs: 1 (f=1): [_(1),M(1)][24.8%][r=20.5MiB/s,w=23.5MiB/s][r=82,w=94 IOPS][eta 01m:31s]
The characters inside the first set of square brackets denote the current status of each thread. The
first character is the first job defined in the job file, and so forth. The possible values (in typical
life cycle order) are:
P Thread setup, but not started.
C Thread created.
I Thread initialized, waiting or generating necessary data.
p Thread running pre-reading file(s).
/ Thread is in ramp period.
R Running, doing sequential reads.
r Running, doing random reads.
W Running, doing sequential writes.
w Running, doing random writes.
M Running, doing mixed sequential reads/writes.
m Running, doing mixed random reads/writes.
D Running, doing sequential trims.
d Running, doing random trims.
F Running, currently waiting for fsync(2).
V Running, doing verification of written data.
f Thread finishing.
E Thread exited, not reaped by main thread yet.
- Thread reaped.
X Thread reaped, exited with an error.
K Thread reaped, exited due to signal.
Fio will condense the thread string as not to take up more space on the command line than needed. For
instance, if you have 10 readers and 10 writers running, the output would look like this:
Jobs: 20 (f=20): [R(10),W(10)][4.0%][r=20.5MiB/s,w=23.5MiB/s][r=82,w=94 IOPS][eta 57m:36s]
Note that the status string is displayed in order, so it's possible to tell which of the jobs are
currently doing what. In the example above this means that jobs 1--10 are readers and 11--20 are writers.
The other values are fairly self explanatory -- number of threads currently running and doing I/O, the
number of currently open files (f=), the estimated completion percentage, the rate of I/O since last
check (read speed listed first, then write speed and optionally trim speed) in terms of bandwidth and
IOPS, and time to completion for the current running group. It's impossible to estimate runtime of the
following groups (if any).
When fio is done (or interrupted by Ctrl-C), it will show the data for each thread, group of threads, and
disks in that order. For each overall thread (or group) the output looks like:
Client1: (groupid=0, jobs=1): err= 0: pid=16109: Sat Jun 24 12:07:54 2017
write: IOPS=88, BW=623KiB/s (638kB/s)(30.4MiB/50032msec)
slat (nsec): min=500, max=145500, avg=8318.00, stdev=4781.50
clat (usec): min=170, max=78367, avg=4019.02, stdev=8293.31
lat (usec): min=174, max=78375, avg=4027.34, stdev=8291.79
clat percentiles (usec):
| 1.00th=[ 302], 5.00th=[ 326], 10.00th=[ 343], 20.00th=[ 363],
| 30.00th=[ 392], 40.00th=[ 404], 50.00th=[ 416], 60.00th=[ 445],
| 70.00th=[ 816], 80.00th=[ 6718], 90.00th=[12911], 95.00th=[21627],
| 99.00th=[43779], 99.50th=[51643], 99.90th=[68682], 99.95th=[72877],
| 99.99th=[78119]
bw ( KiB/s): min= 532, max= 686, per=0.10%, avg=622.87, stdev=24.82, samples= 100
iops : min= 76, max= 98, avg=88.98, stdev= 3.54, samples= 100
lat (usec) : 250=0.04%, 500=64.11%, 750=4.81%, 1000=2.79%
lat (msec) : 2=4.16%, 4=1.84%, 10=4.90%, 20=11.33%, 50=5.37%
lat (msec) : 100=0.65%
cpu : usr=0.27%, sys=0.18%, ctx=12072, majf=0, minf=21
IO depths : 1=85.0%, 2=13.1%, 4=1.8%, 8=0.1%, 16=0.0%, 32=0.0%, >=64=0.0%
submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
issued rwt: total=0,4450,0, short=0,0,0, dropped=0,0,0
latency : target=0, window=0, percentile=100.00%, depth=8
The job name (or first job's name when using group_reporting) is printed, along with the group id, count
of jobs being aggregated, last error id seen (which is 0 when there are no errors), pid/tid of that
thread and the time the job/group completed. Below are the I/O statistics for each data direction
performed (showing writes in the example above). In the order listed, they denote:
read/write/trim
The string before the colon shows the I/O direction the statistics are for. IOPS is the
average I/Os performed per second. BW is the average bandwidth rate shown as: value in
power of 2 format (value in power of 10 format). The last two values show: (total I/O
performed in power of 2 format / runtime of that thread).
slat Submission latency (min being the minimum, max being the maximum, avg being the average,
stdev being the standard deviation). This is the time it took to submit the I/O. For sync
I/O this row is not displayed as the slat is really the completion latency (since
queue/complete is one operation there). This value can be in nanoseconds, microseconds or
milliseconds --- fio will choose the most appropriate base and print that (in the example
above nanoseconds was the best scale). Note: in --minimal mode latencies are always
expressed in microseconds.
clat Completion latency. Same names as slat, this denotes the time from submission to completion
of the I/O pieces. For sync I/O, clat will usually be equal (or very close) to 0, as the
time from submit to complete is basically just CPU time (I/O has already been done, see
slat explanation).
lat Total latency. Same names as slat and clat, this denotes the time from when fio created the
I/O unit to completion of the I/O operation.
bw Bandwidth statistics based on samples. Same names as the xlat stats, but also includes the
number of samples taken (samples) and an approximate percentage of total aggregate
bandwidth this thread received in its group (per). This last value is only really useful if
the threads in this group are on the same disk, since they are then competing for disk
access.
iops IOPS statistics based on samples. Same names as bw.
lat (nsec/usec/msec)
The distribution of I/O completion latencies. This is the time from when I/O leaves fio and
when it gets completed. Unlike the separate read/write/trim sections above, the data here
and in the remaining sections apply to all I/Os for the reporting group. 250=0.04% means
that 0.04% of the I/Os completed in under 250us. 500=64.11% means that 64.11% of the I/Os
required 250 to 499us for completion.
cpu CPU usage. User and system time, along with the number of context switches this thread went
through, usage of system and user time, and finally the number of major and minor page
faults. The CPU utilization numbers are averages for the jobs in that reporting group,
while the context and fault counters are summed.
IO depths
The distribution of I/O depths over the job lifetime. The numbers are divided into powers
of 2 and each entry covers depths from that value up to those that are lower than the next
entry -- e.g., 16= covers depths from 16 to 31. Note that the range covered by a depth
distribution entry can be different to the range covered by the equivalent submit/complete
distribution entry.
IO submit
How many pieces of I/O were submitting in a single submit call. Each entry denotes that
amount and below, until the previous entry -- e.g., 16=100% means that we submitted
anywhere between 9 to 16 I/Os per submit call. Note that the range covered by a submit
distribution entry can be different to the range covered by the equivalent depth
distribution entry.
IO complete
Like the above submit number, but for completions instead.
IO issued rwt
The number of read/write/trim requests issued, and how many of them were short or dropped.
IO latency
These values are for latency_target and related options. When these options are engaged,
this section describes the I/O depth required to meet the specified latency target.
After each client has been listed, the group statistics are printed. They will look like this:
Run status group 0 (all jobs):
READ: bw=20.9MiB/s (21.9MB/s), 10.4MiB/s-10.8MiB/s (10.9MB/s-11.3MB/s), io=64.0MiB (67.1MB), run=2973-3069msec
WRITE: bw=1231KiB/s (1261kB/s), 616KiB/s-621KiB/s (630kB/s-636kB/s), io=64.0MiB (67.1MB), run=52747-53223msec
For each data direction it prints:
bw Aggregate bandwidth of threads in this group followed by the minimum and maximum bandwidth
of all the threads in this group. Values outside of brackets are power-of-2 format and
those within are the equivalent value in a power-of-10 format.
io Aggregate I/O performed of all threads in this group. The format is the same as bw.
run The smallest and longest runtimes of the threads in this group.
And finally, the disk statistics are printed. This is Linux specific. They will look like this:
Disk stats (read/write):
sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
Each value is printed for both reads and writes, with reads first. The numbers denote:
ios Number of I/Os performed by all groups.
merge Number of merges performed by the I/O scheduler.
ticks Number of ticks we kept the disk busy.
in_queue
Total time spent in the disk queue.
util The disk utilization. A value of 100% means we kept the disk busy constantly, 50% would be
a disk idling half of the time.
It is also possible to get fio to dump the current output while it is running, without terminating the
job. To do that, send fio the USR1 signal. You can also get regularly timed dumps by using the
--status-interval parameter, or by creating a file in `/tmp' named `fio-dump-status'. If fio sees this
file, it will unlink it and dump the current output status.
TERSE OUTPUT
For scripted usage where you typically want to generate tables or graphs of the results, fio can output
the results in a semicolon separated format. The format is one long line of values, such as:
2;card0;0;0;7139336;121836;60004;1;10109;27.932460;116.933948;220;126861;3495.446807;1085.368601;226;126864;3523.635629;1089.012448;24063;99944;50.275485%;59818.274627;5540.657370;7155060;122104;60004;1;8338;29.086342;117.839068;388;128077;5032.488518;1234.785715;391;128085;5061.839412;1236.909129;23436;100928;50.287926%;59964.832030;5644.844189;14.595833%;19.394167%;123706;0;7313;0.1%;0.1%;0.1%;0.1%;0.1%;0.1%;100.0%;0.00%;0.00%;0.00%;0.00%;0.00%;0.00%;0.01%;0.02%;0.05%;0.16%;6.04%;40.40%;52.68%;0.64%;0.01%;0.00%;0.01%;0.00%;0.00%;0.00%;0.00%;0.00%
A description of this job goes here.
The job description (if provided) follows on a second line for terse v2. It appears on the same line for
other terse versions.
To enable terse output, use the --minimal or `--output-format=terse' command line options. The first
value is the version of the terse output format. If the output has to be changed for some reason, this
number will be incremented by 1 to signify that change.
Split up, the format is as follows (comments in brackets denote when a field was introduced or whether
it's specific to some terse version):
terse version, fio version [v3], jobname, groupid, error
READ status:
Total IO (KiB), bandwidth (KiB/sec), IOPS, runtime (msec)
Submission latency: min, max, mean, stdev (usec)
Completion latency: min, max, mean, stdev (usec)
Completion latency percentiles: 20 fields (see below)
Total latency: min, max, mean, stdev (usec)
Bw (KiB/s): min, max, aggregate percentage of total, mean, stdev, number of samples [v5]
IOPS [v5]: min, max, mean, stdev, number of samples
WRITE status:
Total IO (KiB), bandwidth (KiB/sec), IOPS, runtime (msec)
Submission latency: min, max, mean, stdev (usec)
Completion latency: min, max, mean, stdev (usec)
Completion latency percentiles: 20 fields (see below)
Total latency: min, max, mean, stdev (usec)
Bw (KiB/s): min, max, aggregate percentage of total, mean, stdev, number of samples [v5]
IOPS [v5]: min, max, mean, stdev, number of samples
TRIM status [all but version 3]:
Fields are similar to READ/WRITE status.
CPU usage:
user, system, context switches, major faults, minor faults
I/O depths:
<=1, 2, 4, 8, 16, 32, >=64
I/O latencies microseconds:
<=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000
I/O latencies milliseconds:
<=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000
Disk utilization [v3]:
disk name, read ios, write ios, read merges, write merges, read ticks, write ticks, time spent in queue, disk utilization percentage
Additional Info (dependent on continue_on_error, default off):
total # errors, first error code
Additional Info (dependent on description being set):
Text description
Completion latency percentiles can be a grouping of up to 20 sets, so for the terse output fio writes all
of them. Each field will look like this:
1.00%=6112
which is the Xth percentile, and the `usec' latency associated with it.
For Disk utilization, all disks used by fio are shown. So for each disk there will be a disk utilization
section.
Below is a single line containing short names for each of the fields in the minimal output v3, separated
by semicolons:
terse_version_3;fio_version;jobname;groupid;error;read_kb;read_bandwidth_kb;read_iops;read_runtime_ms;read_slat_min_us;read_slat_max_us;read_slat_mean_us;read_slat_dev_us;read_clat_min_us;read_clat_max_us;read_clat_mean_us;read_clat_dev_us;read_clat_pct01;read_clat_pct02;read_clat_pct03;read_clat_pct04;read_clat_pct05;read_clat_pct06;read_clat_pct07;read_clat_pct08;read_clat_pct09;read_clat_pct10;read_clat_pct11;read_clat_pct12;read_clat_pct13;read_clat_pct14;read_clat_pct15;read_clat_pct16;read_clat_pct17;read_clat_pct18;read_clat_pct19;read_clat_pct20;read_tlat_min_us;read_lat_max_us;read_lat_mean_us;read_lat_dev_us;read_bw_min_kb;read_bw_max_kb;read_bw_agg_pct;read_bw_mean_kb;read_bw_dev_kb;write_kb;write_bandwidth_kb;write_iops;write_runtime_ms;write_slat_min_us;write_slat_max_us;write_slat_mean_us;write_slat_dev_us;write_clat_min_us;write_clat_max_us;write_clat_mean_us;write_clat_dev_us;write_clat_pct01;write_clat_pct02;write_clat_pct03;write_clat_pct04;write_clat_pct05;write_clat_pct06;write_clat_pct07;write_clat_pct08;write_clat_pct09;write_clat_pct10;write_clat_pct11;write_clat_pct12;write_clat_pct13;write_clat_pct14;write_clat_pct15;write_clat_pct16;write_clat_pct17;write_clat_pct18;write_clat_pct19;write_clat_pct20;write_tlat_min_us;write_lat_max_us;write_lat_mean_us;write_lat_dev_us;write_bw_min_kb;write_bw_max_kb;write_bw_agg_pct;write_bw_mean_kb;write_bw_dev_kb;cpu_user;cpu_sys;cpu_csw;cpu_mjf;cpu_minf;iodepth_1;iodepth_2;iodepth_4;iodepth_8;iodepth_16;iodepth_32;iodepth_64;lat_2us;lat_4us;lat_10us;lat_20us;lat_50us;lat_100us;lat_250us;lat_500us;lat_750us;lat_1000us;lat_2ms;lat_4ms;lat_10ms;lat_20ms;lat_50ms;lat_100ms;lat_250ms;lat_500ms;lat_750ms;lat_1000ms;lat_2000ms;lat_over_2000ms;disk_name;disk_read_iops;disk_write_iops;disk_read_merges;disk_write_merges;disk_read_ticks;write_ticks;disk_queue_time;disk_util
In client/server mode terse output differs from what appears when jobs are run locally. Disk utilization
data is omitted from the standard terse output and for v3 and later appears on its own separate line at
the end of each terse reporting cycle.
JSON OUTPUT
The json output format is intended to be both human readable and convenient for automated parsing. For
the most part its sections mirror those of the normal output. The runtime value is reported in msec and
the bw value is reported in 1024 bytes per second units.
JSON+ OUTPUT
The json+ output format is identical to the json output format except that it adds a full dump of the
completion latency bins. Each bins object contains a set of (key, value) pairs where keys are latency
durations and values count how many I/Os had completion latencies of the corresponding duration. For
example, consider:
"bins" : { "87552" : 1, "89600" : 1, "94720" : 1, "96768" : 1, "97792" : 1, "99840" : 1, "100864"
: 2, "103936" : 6, "104960" : 534, "105984" : 5995, "107008" : 7529, ... }
This data indicates that one I/O required 87,552ns to complete, two I/Os required 100,864ns to complete,
and 7529 I/Os required 107,008ns to complete.
Also included with fio is a Python script fio_jsonplus_clat2csv that takes json+ output and generates
CSV-formatted latency data suitable for plotting.
The latency durations actually represent the midpoints of latency intervals. For details refer to
`stat.h' in the fio source.
TRACE FILE FORMAT
There are two trace file format that you can encounter. The older (v1) format is unsupported since
version 1.20-rc3 (March 2008). It will still be described below in case that you get an old trace and
want to understand it.
In any case the trace is a simple text file with a single action per line.
Trace file format v1
Each line represents a single I/O action in the following format:
rw, offset, length
where `rw=0/1' for read/write, and the `offset' and `length' entries being in bytes.
This format is not supported in fio versions >= 1.20-rc3.
Trace file format v2
The second version of the trace file format was added in fio version 1.17. It allows to access
more then one file per trace and has a bigger set of possible file actions.
The first line of the trace file has to be:
"fio version 2 iolog"
Following this can be lines in two different formats, which are described below.
The file management format:
filename action
The `filename' is given as an absolute path. The `action' can be one of these:
add Add the given `filename' to the trace.
open Open the file with the given `filename'. The `filename' has to have been
added with the add action before.
close Close the file with the given `filename'. The file has to have been opened
before.
The file I/O action format:
filename action offset length
The `filename' is given as an absolute path, and has to have been added and opened before
it can be used with this format. The `offset' and `length' are given in bytes. The `action'
can be one of these:
wait Wait for `offset' microseconds. Everything below 100 is discarded. The time
is relative to the previous `wait' statement.
read Read `length' bytes beginning from `offset'.
write Write `length' bytes beginning from `offset'.
sync fsync(2) the file.
datasync
fdatasync(2) the file.
trim Trim the given file from the given `offset' for `length' bytes.
I/O REPLAY - MERGING TRACES
Colocation is a common practice used to get the most out of a machine. Knowing which workloads play
nicely with each other and which ones don't is a much harder task. While fio can replay workloads
concurrently via multiple jobs, it leaves some variability up to the scheduler making results harder to
reproduce. Merging is a way to make the order of events consistent.
Merging is integrated into I/O replay and done when a merge_blktrace_file is specified. The list of files
passed to read_iolog go through the merge process and output a single file stored to the specified file.
The output file is passed on as if it were the only file passed to read_iolog. An example would look
like:
$ fio --read_iolog="<file1>:<file2>" --merge_blktrace_file="<output_file>"
Creating only the merged file can be done by passing the command line argument merge-blktrace-only.
Scaling traces can be done to see the relative impact of any particular trace being slowed down or sped
up. merge_blktrace_scalars takes in a colon separated list of percentage scalars. It is index paired with
the files passed to read_iolog.
With scaling, it may be desirable to match the running time of all traces. This can be done with
merge_blktrace_iters. It is index paired with read_iolog just like merge_blktrace_scalars.
In an example, given two traces, A and B, each 60s long. If we want to see the impact of trace A issuing
IOs twice as fast and repeat trace A over the runtime of trace B, the following can be done:
$ fio --read_iolog="<trace_a>:"<trace_b>" --merge_blktrace_file"<output_file>"
--merge_blktrace_scalars="50:100" --merge_blktrace_iters="2:1"
This runs trace A at 2x the speed twice for approximately the same runtime as a single run of trace B.
CPU IDLENESS PROFILING
In some cases, we want to understand CPU overhead in a test. For example, we test patches for the
specific goodness of whether they reduce CPU usage. Fio implements a balloon approach to create a thread
per CPU that runs at idle priority, meaning that it only runs when nobody else needs the cpu. By
measuring the amount of work completed by the thread, idleness of each CPU can be derived accordingly.
An unit work is defined as touching a full page of unsigned characters. Mean and standard deviation of
time to complete an unit work is reported in "unit work" section. Options can be chosen to report
detailed percpu idleness or overall system idleness by aggregating percpu stats.
VERIFICATION AND TRIGGERS
Fio is usually run in one of two ways, when data verification is done. The first is a normal write job of
some sort with verify enabled. When the write phase has completed, fio switches to reads and verifies
everything it wrote. The second model is running just the write phase, and then later on running the same
job (but with reads instead of writes) to repeat the same I/O patterns and verify the contents. Both of
these methods depend on the write phase being completed, as fio otherwise has no idea how much data was
written.
With verification triggers, fio supports dumping the current write state to local files. Then a
subsequent read verify workload can load this state and know exactly where to stop. This is useful for
testing cases where power is cut to a server in a managed fashion, for instance.
A verification trigger consists of two things:
1) Storing the write state of each job.
2) Executing a trigger command.
The write state is relatively small, on the order of hundreds of bytes to single kilobytes. It contains
information on the number of completions done, the last X completions, etc.
A trigger is invoked either through creation ('touch') of a specified file in the system, or through a
timeout setting. If fio is run with `--trigger-file=/tmp/trigger-file', then it will continually check
for the existence of `/tmp/trigger-file'. When it sees this file, it will fire off the trigger (thus
saving state, and executing the trigger command).
For client/server runs, there's both a local and remote trigger. If fio is running as a server backend,
it will send the job states back to the client for safe storage, then execute the remote trigger, if
specified. If a local trigger is specified, the server will still send back the write state, but the
client will then execute the trigger.
Verification trigger example
Let's say we want to run a powercut test on the remote Linux machine 'server'. Our write workload
is in `write-test.fio'. We want to cut power to 'server' at some point during the run, and we'll
run this test from the safety or our local machine, 'localbox'. On the server, we'll start the fio
backend normally:
server# fio --server
and on the client, we'll fire off the workload:
localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trigger-remote="bash -c
"echo b > /proc/sysrq-triger""
We set `/tmp/my-trigger' as the trigger file, and we tell fio to execute:
echo b > /proc/sysrq-trigger
on the server once it has received the trigger and sent us the write state. This will work, but
it's not really cutting power to the server, it's merely abruptly rebooting it. If we have a
remote way of cutting power to the server through IPMI or similar, we could do that through a
local trigger command instead. Let's assume we have a script that does IPMI reboot of a given
hostname, ipmi-reboot. On localbox, we could then have run fio with a local trigger instead:
localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trigger="ipmi-reboot server"
For this case, fio would wait for the server to send us the write state, then execute `ipmi-reboot
server' when that happened.
Loading verify state
To load stored write state, a read verification job file must contain the verify_state_load
option. If that is set, fio will load the previously stored state. For a local fio run this is
done by loading the files directly, and on a client/server run, the server backend will ask the
client to send the files over and load them from there.
LOG FILE FORMATS
Fio supports a variety of log file formats, for logging latencies, bandwidth, and IOPS. The logs share a
common format, which looks like this:
time (msec), value, data direction, block size (bytes), offset (bytes), command priority
`Time' for the log entry is always in milliseconds. The `value' logged depends on the type of log, it
will be one of the following:
Latency log
Value is latency in nsecs
Bandwidth log
Value is in KiB/sec
IOPS log
Value is IOPS
`Data direction' is one of the following:
0 I/O is a READ
1 I/O is a WRITE
2 I/O is a TRIM
The entry's `block size' is always in bytes. The `offset' is the position in bytes from the start of the
file for that particular I/O. The logging of the offset can be toggled with log_offset.
If log_prio is not set, the entry's `Command priority` is 1 for an IO executed with the highest RT
priority class (prioclass=1 or cmdprio_class=1) and 0 otherwise. This is controlled by the prioclass
option and the ioengine specific cmdprio_percentage cmdprio_class options. If log_prio is set, the
entry's `Command priority` is the priority set for the IO, as a 16-bits hexadecimal number with the
lowest 13 bits indicating the priority value (prio and cmdprio options) and the highest 3 bits indicating
the IO priority class (prioclass and cmdprio_class options).
Fio defaults to logging every individual I/O but when windowed logging is set through log_avg_msec,
either the average (by default) or the maximum (log_max_value is set) `value' seen over the specified
period of time is recorded. Each `data direction' seen within the window period will aggregate its values
in a separate row. Further, when using windowed logging the `block size' and `offset' entries will always
contain 0.
CLIENT / SERVER
Normally fio is invoked as a stand-alone application on the machine where the I/O workload should be
generated. However, the backend and frontend of fio can be run separately i.e., the fio server can
generate an I/O workload on the "Device Under Test" while being controlled by a client on another
machine.
Start the server on the machine which has access to the storage DUT:
$ fio --server=args
where `args' defines what fio listens to. The arguments are of the form `type,hostname' or `IP,port'.
`type' is either `ip' (or ip4) for TCP/IP v4, `ip6' for TCP/IP v6, or `sock' for a local unix domain
socket. `hostname' is either a hostname or IP address, and `port' is the port to listen to (only valid
for TCP/IP, not a local socket). Some examples:
1) fio --server
Start a fio server, listening on all interfaces on the default port (8765).
2) fio --server=ip:hostname,4444
Start a fio server, listening on IP belonging to hostname and on port 4444.
3) fio --server=ip6:::1,4444
Start a fio server, listening on IPv6 localhost ::1 and on port 4444.
4) fio --server=,4444
Start a fio server, listening on all interfaces on port 4444.
5) fio --server=1.2.3.4
Start a fio server, listening on IP 1.2.3.4 on the default port.
6) fio --server=sock:/tmp/fio.sock
Start a fio server, listening on the local socket `/tmp/fio.sock'.
Once a server is running, a "client" can connect to the fio server with:
$ fio <local-args> --client=<server> <remote-args> <job file(s)>
where `local-args' are arguments for the client where it is running, `server' is the connect string, and
`remote-args' and `job file(s)' are sent to the server. The `server' string follows the same format as it
does on the server side, to allow IP/hostname/socket and port strings.
Fio can connect to multiple servers this way:
$ fio --client=<server1> <job file(s)> --client=<server2> <job file(s)>
If the job file is located on the fio server, then you can tell the server to load a local file as well.
This is done by using --remote-config:
$ fio --client=server --remote-config /path/to/file.fio
Then fio will open this local (to the server) job file instead of being passed one from the client.
If you have many servers (example: 100 VMs/containers), you can input a pathname of a file containing
host IPs/names as the parameter value for the --client option. For example, here is an example
`host.list' file containing 2 hostnames:
host1.your.dns.domain
host2.your.dns.domain
The fio command would then be:
$ fio --client=host.list <job file(s)>
In this mode, you cannot input server-specific parameters or job files -- all servers receive the same
job file.
In order to let `fio --client' runs use a shared filesystem from multiple hosts, `fio --client' now
prepends the IP address of the server to the filename. For example, if fio is using the directory
`/mnt/nfs/fio' and is writing filename `fileio.tmp', with a --client `hostfile' containing two hostnames
`h1' and `h2' with IP addresses 192.168.10.120 and 192.168.10.121, then fio will create two files:
/mnt/nfs/fio/192.168.10.120.fileio.tmp
/mnt/nfs/fio/192.168.10.121.fileio.tmp
Terse output in client/server mode will differ slightly from what is produced when fio is run in stand-
alone mode. See the terse output section for details.
AUTHORS
fio was written by Jens Axboe <axboe@kernel.dk>.
This man page was written by Aaron Carroll <aaronc@cse.unsw.edu.au> based on documentation by Jens Axboe.
This man page was rewritten by Tomohiro Kusumi <tkusumi@tuxera.com> based on documentation by Jens Axboe.
REPORTING BUGS
Report bugs to the fio mailing list <fio@vger.kernel.org>.
See REPORTING-BUGS.
REPORTING-BUGS: http://git.kernel.dk/cgit/fio/plain/REPORTING-BUGS
SEE ALSO
For further documentation see HOWTO and README.
Sample jobfiles are available in the `examples/' directory.
These are typically located under `/usr/share/doc/fio'.
HOWTO: http://git.kernel.dk/cgit/fio/plain/HOWTO
README: http://git.kernel.dk/cgit/fio/plain/README
User Manual August 2017 fio(1)