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.

HARDWARE
The nda driver supports NVMe (Non-Volatile Memory Express) storage devices connected via PCIe or over NVMF (NVMe over Fabric) via 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>