• Damien Le Moal's avatar
    dm zoned: drive-managed zoned block device target · 3b1a94c8
    Damien Le Moal authored
    The dm-zoned device mapper target provides transparent write access
    to zoned block devices (ZBC and ZAC compliant block devices).
    dm-zoned hides to the device user (a file system or an application
    doing raw block device accesses) any constraint imposed on write
    requests by the device, equivalent to a drive-managed zoned block
    device model.
    Write requests are processed using a combination of on-disk buffering
    using the device conventional zones and direct in-place processing for
    requests aligned to a zone sequential write pointer position.
    A background reclaim process implemented using dm_kcopyd_copy ensures
    that conventional zones are always available for executing unaligned
    write requests. The reclaim process overhead is minimized by managing
    buffer zones in a least-recently-written order and first targeting the
    oldest buffer zones. Doing so, blocks under regular write access (such
    as metadata blocks of a file system) remain stored in conventional
    zones, resulting in no apparent overhead.
    dm-zoned implementation focus on simplicity and on minimizing overhead
    (CPU, memory and storage overhead). For a 14TB host-managed disk with
    256 MB zones, dm-zoned memory usage per disk instance is at most about
    3 MB and as little as 5 zones will be used internally for storing metadata
    and performing buffer zone reclaim operations. This is achieved using
    zone level indirection rather than a full block indirection system for
    managing block movement between zones.
    dm-zoned primary target is host-managed zoned block devices but it can
    also be used with host-aware device models to mitigate potential
    device-side performance degradation due to excessive random writing.
    Zoned block devices can be formatted and checked for use with the dm-zoned
    target using the dmzadm utility available at:
    https://github.com/hgst/dm-zoned-toolsSigned-off-by: default avatarDamien Le Moal <damien.lemoal@wdc.com>
    Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
    Reviewed-by: default avatarBart Van Assche <bart.vanassche@sandisk.com>
    [Mike Snitzer partly refactored Damien's original work to cleanup the code]
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
dm-zoned.txt 6.65 KB