208 lines
5.9 KiB
Groff
208 lines
5.9 KiB
Groff
.\"
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.\" Copyright (c) 2017 Netflix, Inc.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\"
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd June 6, 2020
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.Dt NDA 4
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.Os
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.Sh NAME
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.Nm nda
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.Nd NVMe Direct Access device driver
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.Sh SYNOPSIS
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.Cd device nvme
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.Cd device scbus
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.Sh DESCRIPTION
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The
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.Nm
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driver provides support for direct access devices, implementing the
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.Tn NVMe
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command protocol, that are attached to the system through a host adapter
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supported by the CAM subsystem.
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.Sh SYSCTL VARIABLES
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The following variables are available as both
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.Xr sysctl 8
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variables and
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.Xr loader 8
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tunables:
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.Bl -tag -width 12
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.It Va hw.nvme.use_nvd
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The
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.Xr nvme 4
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driver will create
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.Nm
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device nodes for block storage when set to 0.
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Create
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.Xr nvd 4
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device nodes for block storage when set to 1.
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See
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.Xr nvd 4
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when set to 1.
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.It Va kern.cam.nda.nvd_compat
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When set to 1,
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.Xr nvd 4
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aliases will be created for all
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.Nm
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devices, including partitions and other
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.Xr geom 4
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providers that take their names from the disk's name.
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.Xr nvd
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devices will not, however, be reported in the
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.Va kern.disks
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.Xr sysctl 8 .
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.It Va kern.cam.nda.sort_io_queue
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This variable determines whether the software queued entries are
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sorted in LBA order or not.
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Sorting is almost always a waste of time.
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The default is to not sort.
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.It Va kern.cam.nda.enable_biospeedup
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This variable determines if the
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.Nm
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devices participate in the speedup protocol.
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When the device participates in the speedup, then when the upper layers
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send a
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.Va BIO_SPEEDUP ,
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all current
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.Va BIO_DELETE
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requests not yet sent to the hardware are completed successfully immediate
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without sending them to the hardware.
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Used in low disk space scenarios when the filesystem encounters
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a critical shortage and needs blocks immediately.
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Since trims have maximum benefit when the LBA is unused for a long time,
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skipping the trim when space is needed for immediate writes results in little to
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no excess wear.
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When participation is disabled,
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.Va BIO_SPEEDUP
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requests are ignored.
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.It Va kern.cam.nda.max_trim
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The maximum number of LBA ranges to be collected together for each DSM trims
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send to the hardware.
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Defaults to 256, which is the maximum number of ranges the protocol supports.
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Sometimes poor trim performance can be mitigated by limiting the number of
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ranges sent to the device.
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This value must be between 1 and 256 inclusive.
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.El
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.Pp
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The following report per-device settings, and are read-only unless
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otherwise indicated.
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Replace
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.Va N
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with the device unit number.
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.Bl -tag -width 12
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.It Va kern.cam.nda.N.rotating
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This variable reports whether the storage volume is spinning or
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flash.
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Its value is hard coded to 0 indicating flash.
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.It Va kern.cam.nda.N.unmapped_io
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This variable reports whether the
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.Nm
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driver accepts unmapped I/O for this unit.
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.It Va kern.cam.nda.N.flags
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This variable reports the current flags.
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.Bl -tag -width 12
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.It Va OPEN
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The device is open.
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.It Va DIRTY
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Set when a write to the drive is scheduled.
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Cleared after flush commands.
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.It Va SCTX_INIT
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Internal flag set after
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.Xr sysctl 8
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nodes have been created.
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.El
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.It Va kern.cam.nda.N.sort_io_queue
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Same as the
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.Va kern.cam.nda.sort_io_queue
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tunable.
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.It Va kern.cam.nda.N.trim_ticks
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Writable.
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When greater than zero, hold trims for up to this many ticks before sending
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to the drive.
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Sometimes waiting a little bit to collect more trims to send at one time
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improves trim performance.
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When 0, no delaying of trims are done.
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.It Va kern.cam.nda.N.trim_goal
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Writable.
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When delaying a bit to collect multiple trims, send the accumulated DSM TRIM to
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the drive.
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.It Va kern.cam.nda.N.trim_lbas
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Total number of LBAs that have been trimmed.
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.It Va kern.cam.nda.N.trim_ranges
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Total number of LBA ranges that have been trimmed.
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.It Va kern.cam.nda.N.trim_count
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Total number of trims sent to the hardware.
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.It Va kern.cam.nda.N.deletes
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Total number of
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.Va BIO_DELETE
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requests queued to the device.
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.El
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.Sh NAMESPACE MAPPING
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Each
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.Xr nvme 4
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drive has one or more namespaces associated with it.
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One instance of the
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.Nm
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driver will be created for each of the namespaces on
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the drive.
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All the
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.Nm
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nodes for a
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.Xr nvme 4
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device are at target 0.
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However, the namespace ID maps to the CAM lun, as reported
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in kernel messages and in the
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.Va devlist
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sub command of
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.Xr camcontrol 8 .
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.Pp
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Namespaces are managed with the
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.Va ns
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sub command of
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.Xr nvmecontrol 8 .
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Not all drives support namespace management,
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but all drives support at least one namespace.
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Device nodes for
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.Nm
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will be created and destroyed dynamically as
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namespaces are activated or detached.
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.Sh FILES
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.Bl -tag -width ".Pa /dev/nda*" -compact
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.It Pa /dev/nda*
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NVMe storage device nodes
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.El
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.Sh SEE ALSO
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.Xr cam 4 ,
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.Xr geom 4 ,
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.Xr nvd 4 ,
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.Xr nvme 4 ,
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.Xr gpart 8
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.Sh HISTORY
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The
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.Nm
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driver first appeared in
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.Fx 12.0 .
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.Sh AUTHORS
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.An Warner Losh Aq Mt imp@FreeBSD.org
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