NDA(4)                 FreeBSD Kernel Interfaces Manual                 NDA(4)

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(4) 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>

FreeBSD 13.1-RELEASE-p6          June 6, 2020          FreeBSD 13.1-RELEASE-p6