NAME

       nda — NVMe Direct Access device driver

SYNOPSIS

       device nvme
       device scbus

DESCRIPTION

       The  nda  driver provides support for direct access devices, implementing the NVMe command protocol, that
       are attached to the system through a host adapter supported by the CAM subsystem.

SYSCTL VARIABLES

       The following variables are available as both sysctl(8) variables and loader(8) tunables:

       hw.nvme.use_nvd
           The nvme(4) driver will create nda device nodes for block storage  when  set  to  0.   Create  nvd(4)
           device nodes for block storage when set to 1.  See nvd(4) when set to 1.

       kern.cam.nda.nvd_compat
           When  set  to  1,  nvd(4) aliases will be created for all nda devices, including partitions and other
           geom(4) providers that take their names from the disk's name.  nvd  devices  will  not,  however,  be
           reported in the kern.disks sysctl(8).

       kern.cam.nda.sort_io_queue
           This variable determines whether the software queued entries are sorted in LBA order or not.  Sorting
           is almost always a waste of time.  The default is to not sort.

       kern.cam.nda.enable_biospeedup
           This  variable  determines  if  the nda devices participate in the speedup protocol.  When the device
           participates in the speedup, then when the upper layers send a BIO_SPEEDUP,  all  current  BIO_DELETE
           requests  not  yet  sent to the hardware are completed successfully immediate without sending them to
           the hardware.  Used in low disk space scenarios when the filesystem encounters  a  critical  shortage
           and  needs  blocks  immediately.   Since trims have maximum benefit when the LBA is unused for a long
           time, skipping the trim when space is needed for immediate writes results  in  little  to  no  excess
           wear.  When participation is disabled, BIO_SPEEDUP requests are ignored.

       kern.cam.nda.max_trim
           The  maximum  number  of LBA ranges to be collected together for each DSM trims send to the hardware.
           Defaults to 256, which is the maximum number of ranges the protocol supports.   Sometimes  poor  trim
           performance can be mitigated by limiting the number of ranges sent to the device.  This value must be
           between 1 and 256 inclusive.

       The  following  report per-device settings, and are read-only unless otherwise indicated.  Replace N with
       the device unit number.

       kern.cam.nda.N.rotating
           This variable reports whether the storage volume is spinning or flash.  Its value is hard coded to  0
           indicating flash.

       kern.cam.nda.N.unmapped_io
           This variable reports whether the nda driver accepts unmapped I/O for this unit.

       kern.cam.nda.N.flags
           This variable reports the current flags.

           OPEN
               The device is open.

           DIRTY
               Set when a write to the drive is scheduled.  Cleared after flush commands.

           SCTX_INIT
               Internal flag set after sysctl(8) nodes have been created.

       kern.cam.nda.N.sort_io_queue
           Same as the kern.cam.nda.sort_io_queue tunable.

       kern.cam.nda.N.trim_ticks
           Writable.   When greater than zero, hold trims for up to this many ticks before sending to the drive.
           Sometimes waiting a little bit to collect more trims to send at one time improves  trim  performance.
           When 0, no delaying of trims are done.

       kern.cam.nda.N.trim_goal
           Writable.  When delaying a bit to collect multiple trims, send the accumulated DSM TRIM to the drive.

       kern.cam.nda.N.trim_lbas
           Total number of LBAs that have been trimmed.

       kern.cam.nda.N.trim_ranges
           Total number of LBA ranges that have been trimmed.

       kern.cam.nda.N.trim_count
           Total number of trims sent to the hardware.

       kern.cam.nda.N.deletes
           Total number of BIO_DELETE requests queued to the device.

NAMESPACE MAPPING

       Each nvme(4) drive has one or more namespaces associated with it.  One instance of the nda driver will be
       created for each of the namespaces on the drive.  All the nda nodes for a nvme(4) device are at target 0.
       However,  the  namespace  ID  maps  to the CAM lun, as reported in kernel messages and in the devlist sub
       command of camcontrol(8).

       Namespaces are managed with the ns sub command of  nvmecontrol(8).   Not  all  drives  support  namespace
       management,  but  all  drives  support  at least one namespace.  Device nodes for nda will be created and
       destroyed dynamically as namespaces are activated or detached.

FILES

       /dev/nda*  NVMe storage device nodes

SEE ALSO

       cam(4), geom(4), nvd(4), nvme(4), gpart(8)

HISTORY

       The nda driver first appeared in FreeBSD 12.0.

AUTHORS

       Warner Losh <imp@FreeBSD.org>

Debian                                            June 6, 2020                                            NDA(4)