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1Device-mapper RAID (dm-raid) is a bridge from DM to MD. It
2provides a way to use device-mapper interfaces to access the MD RAID
3drivers.
4
5As with all device-mapper targets, the nominal public interfaces are the
6constructor (CTR) tables and the status outputs (both STATUSTYPE_INFO
7and STATUSTYPE_TABLE). The CTR table looks like the following:
8
91: <s> <l> raid \
102: <raid_type> <#raid_params> <raid_params> \
113: <#raid_devs> <meta_dev1> <dev1> .. <meta_devN> <devN>
12
13Line 1 contains the standard first three arguments to any device-mapper
14target - the start, length, and target type fields. The target type in
15this case is "raid".
16
17Line 2 contains the arguments that define the particular raid
18type/personality/level, the required arguments for that raid type, and
19any optional arguments. Possible raid types include: raid4, raid5_la,
20raid5_ls, raid5_rs, raid6_zr, raid6_nr, and raid6_nc. (raid1 is
21planned for the future.) The list of required and optional parameters
22is the same for all the current raid types. The required parameters are
23positional, while the optional parameters are given as key/value pairs.
24The possible parameters are as follows:
25 <chunk_size> Chunk size in sectors.
26 [[no]sync] Force/Prevent RAID initialization
27 [rebuild <idx>] Rebuild the drive indicated by the index
28 [daemon_sleep <ms>] Time between bitmap daemon work to clear bits
29 [min_recovery_rate <kB/sec/disk>] Throttle RAID initialization
30 [max_recovery_rate <kB/sec/disk>] Throttle RAID initialization
31 [max_write_behind <sectors>] See '-write-behind=' (man mdadm)
32 [stripe_cache <sectors>] Stripe cache size for higher RAIDs
33
34Line 3 contains the list of devices that compose the array in
35metadata/data device pairs. If the metadata is stored separately, a '-'
36is given for the metadata device position. If a drive has failed or is
37missing at creation time, a '-' can be given for both the metadata and
38data drives for a given position.
39
40NB. Currently all metadata devices must be specified as '-'.
41
42Examples:
43# RAID4 - 4 data drives, 1 parity
44# No metadata devices specified to hold superblock/bitmap info
45# Chunk size of 1MiB
46# (Lines separated for easy reading)
470 1960893648 raid \
48 raid4 1 2048 \
49 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81
50
51# RAID4 - 4 data drives, 1 parity (no metadata devices)
52# Chunk size of 1MiB, force RAID initialization,
53# min recovery rate at 20 kiB/sec/disk
540 1960893648 raid \
55 raid4 4 2048 min_recovery_rate 20 sync\
56 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81
57
58Performing a 'dmsetup table' should display the CTR table used to
59construct the mapping (with possible reordering of optional
60parameters).
61
62Performing a 'dmsetup status' will yield information on the state and
63health of the array. The output is as follows:
641: <s> <l> raid \
652: <raid_type> <#devices> <1 health char for each dev> <resync_ratio>
66
67Line 1 is standard DM output. Line 2 is best shown by example:
68 0 1960893648 raid raid4 5 AAAAA 2/490221568
69Here we can see the RAID type is raid4, there are 5 devices - all of
70which are 'A'live, and the array is 2/490221568 complete with recovery.