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