LXR linux/Documentation/device-mapper/dm-raid.txt

   1dm-raid
   2-------
   3
   4The device-mapper RAID (dm-raid) target provides a bridge from DM to MD.
   5It allows the MD RAID drivers to be accessed using a device-mapper
   6interface.
   7
   8The target is named "raid" and it accepts the following parameters:
   9
  10  <raid_type> <#raid_params> <raid_params> \
  11    <#raid_devs> <metadata_dev0> <dev0> [.. <metadata_devN> <devN>]
  12
  13<raid_type>:
  14  raid1         RAID1 mirroring
  15  raid4         RAID4 dedicated parity disk
  16  raid5_la      RAID5 left asymmetric
  17                - rotating parity 0 with data continuation
  18  raid5_ra      RAID5 right asymmetric
  19                - rotating parity N with data continuation
  20  raid5_ls      RAID5 left symmetric
  21                - rotating parity 0 with data restart
  22  raid5_rs      RAID5 right symmetric
  23                - rotating parity N with data restart
  24  raid6_zr      RAID6 zero restart
  25                - rotating parity zero (left-to-right) with data restart
  26  raid6_nr      RAID6 N restart
  27                - rotating parity N (right-to-left) with data restart
  28  raid6_nc      RAID6 N continue
  29                - rotating parity N (right-to-left) with data continuation
  30
  31  Refererence: Chapter 4 of
  32  http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf
  33
  34<#raid_params>: The number of parameters that follow.
  35
  36<raid_params> consists of
  37    Mandatory parameters:
  38        <chunk_size>: Chunk size in sectors.  This parameter is often known as
  39                      "stripe size".  It is the only mandatory parameter and
  40                      is placed first.
  41
  42    followed by optional parameters (in any order):
  43        [sync|nosync]   Force or prevent RAID initialization.
  44
  45        [rebuild <idx>] Rebuild drive number idx (first drive is 0).
  46
  47        [daemon_sleep <ms>]
  48                Interval between runs of the bitmap daemon that
  49                clear bits.  A longer interval means less bitmap I/O but
  50                resyncing after a failure is likely to take longer.
  51
  52        [min_recovery_rate <kB/sec/disk>]  Throttle RAID initialization
  53        [max_recovery_rate <kB/sec/disk>]  Throttle RAID initialization
  54        [write_mostly <idx>]               Drive index is write-mostly
  55        [max_write_behind <sectors>]       See '-write-behind=' (man mdadm)
  56        [stripe_cache <sectors>]           Stripe cache size (higher RAIDs only)
  57        [region_size <sectors>]
  58                The region_size multiplied by the number of regions is the
  59                logical size of the array.  The bitmap records the device
  60                synchronisation state for each region.
  61
  62<#raid_devs>: The number of devices composing the array.
  63        Each device consists of two entries.  The first is the device
  64        containing the metadata (if any); the second is the one containing the
  65        data.
  66
  67        If a drive has failed or is missing at creation time, a '-' can be
  68        given for both the metadata and data drives for a given position.
  69
  70
  71Example tables
  72--------------
  73# RAID4 - 4 data drives, 1 parity (no metadata devices)
  74# No metadata devices specified to hold superblock/bitmap info
  75# Chunk size of 1MiB
  76# (Lines separated for easy reading)
  77
  780 1960893648 raid \
  79        raid4 1 2048 \
  80        5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81
  81
  82# RAID4 - 4 data drives, 1 parity (with metadata devices)
  83# Chunk size of 1MiB, force RAID initialization,
  84#       min recovery rate at 20 kiB/sec/disk
  85
  860 1960893648 raid \
  87        raid4 4 2048 sync min_recovery_rate 20 \
  88        5 8:17 8:18 8:33 8:34 8:49 8:50 8:65 8:66 8:81 8:82
  89
  90'dmsetup table' displays the table used to construct the mapping.
  91The optional parameters are always printed in the order listed
  92above with "sync" or "nosync" always output ahead of the other
  93arguments, regardless of the order used when originally loading the table.
  94Arguments that can be repeated are ordered by value.
  95
  96'dmsetup status' yields information on the state and health of the
  97array.
  98The output is as follows:
  991: <s> <l> raid \
 1002:      <raid_type> <#devices> <1 health char for each dev> <resync_ratio>
 101
 102Line 1 is the standard output produced by device-mapper.
 103Line 2 is produced by the raid target, and best explained by example:
 104        0 1960893648 raid raid4 5 AAAAA 2/490221568
 105Here we can see the RAID type is raid4, there are 5 devices - all of
 106which are 'A'live, and the array is 2/490221568 complete with recovery.
 107Faulty or missing devices are marked 'D'.  Devices that are out-of-sync
 108are marked 'a'.
 109