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>