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Documentation / device-mapper / dm-raid.txt




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Based on kernel version 3.3. Page generated on 2012-03-23 21:25 EST.

1	dm-raid
2	-------
3	
4	The device-mapper RAID (dm-raid) target provides a bridge from DM to MD.
5	It allows the MD RAID drivers to be accessed using a device-mapper
6	interface.
7	
8	The 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	
71	Example 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	
78	0 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	
86	0 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.
91	The optional parameters are always printed in the order listed
92	above with "sync" or "nosync" always output ahead of the other
93	arguments, regardless of the order used when originally loading the table.
94	Arguments that can be repeated are ordered by value.
95	
96	'dmsetup status' yields information on the state and health of the
97	array.
98	The output is as follows:
99	1: <s> <l> raid \
100	2:      <raid_type> <#devices> <1 health char for each dev> <resync_ratio>
101	
102	Line 1 is the standard output produced by device-mapper.
103	Line 2 is produced by the raid target, and best explained by example:
104	        0 1960893648 raid raid4 5 AAAAA 2/490221568
105	Here we can see the RAID type is raid4, there are 5 devices - all of
106	which are 'A'live, and the array is 2/490221568 complete with recovery.
107	Faulty or missing devices are marked 'D'.  Devices that are out-of-sync
108	are marked 'a'.
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