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1 | dm-raid |
2 | ------- | |
9d09e663 | 3 | |
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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. | |
9d09e663 | 7 | |
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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>: | |
b12d437b | 14 | raid1 RAID1 mirroring |
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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 | |
63f33b8d JB |
30 | raid10 Various RAID10 inspired algorithms chosen by additional params |
31 | - RAID10: Striped Mirrors (aka 'Striping on top of mirrors') | |
32 | - RAID1E: Integrated Adjacent Stripe Mirroring | |
33 | - and other similar RAID10 variants | |
c0a2fa1e | 34 | |
40e47125 | 35 | Reference: Chapter 4 of |
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36 | http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf |
37 | ||
38 | <#raid_params>: The number of parameters that follow. | |
39 | ||
40 | <raid_params> consists of | |
41 | Mandatory parameters: | |
42 | <chunk_size>: Chunk size in sectors. This parameter is often known as | |
43 | "stripe size". It is the only mandatory parameter and | |
44 | is placed first. | |
45 | ||
46 | followed by optional parameters (in any order): | |
47 | [sync|nosync] Force or prevent RAID initialization. | |
48 | ||
49 | [rebuild <idx>] Rebuild drive number idx (first drive is 0). | |
50 | ||
51 | [daemon_sleep <ms>] | |
52 | Interval between runs of the bitmap daemon that | |
53 | clear bits. A longer interval means less bitmap I/O but | |
54 | resyncing after a failure is likely to take longer. | |
55 | ||
56 | [min_recovery_rate <kB/sec/disk>] Throttle RAID initialization | |
57 | [max_recovery_rate <kB/sec/disk>] Throttle RAID initialization | |
46bed2b5 | 58 | [write_mostly <idx>] Drive index is write-mostly |
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59 | [max_write_behind <sectors>] See '-write-behind=' (man mdadm) |
60 | [stripe_cache <sectors>] Stripe cache size (higher RAIDs only) | |
c1084561 JB |
61 | [region_size <sectors>] |
62 | The region_size multiplied by the number of regions is the | |
63 | logical size of the array. The bitmap records the device | |
64 | synchronisation state for each region. | |
c0a2fa1e | 65 | |
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66 | [raid10_copies <# copies>] |
67 | [raid10_format near] | |
68 | These two options are used to alter the default layout of | |
69 | a RAID10 configuration. The number of copies is can be | |
70 | specified, but the default is 2. There are other variations | |
71 | to how the copies are laid down - the default and only current | |
72 | option is "near". Near copies are what most people think of | |
73 | with respect to mirroring. If these options are left | |
74 | unspecified, or 'raid10_copies 2' and/or 'raid10_format near' | |
75 | are given, then the layouts for 2, 3 and 4 devices are: | |
76 | 2 drives 3 drives 4 drives | |
77 | -------- ---------- -------------- | |
78 | A1 A1 A1 A1 A2 A1 A1 A2 A2 | |
79 | A2 A2 A2 A3 A3 A3 A3 A4 A4 | |
80 | A3 A3 A4 A4 A5 A5 A5 A6 A6 | |
81 | A4 A4 A5 A6 A6 A7 A7 A8 A8 | |
82 | .. .. .. .. .. .. .. .. .. | |
83 | The 2-device layout is equivalent 2-way RAID1. The 4-device | |
84 | layout is what a traditional RAID10 would look like. The | |
85 | 3-device layout is what might be called a 'RAID1E - Integrated | |
86 | Adjacent Stripe Mirroring'. | |
87 | ||
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88 | <#raid_devs>: The number of devices composing the array. |
89 | Each device consists of two entries. The first is the device | |
90 | containing the metadata (if any); the second is the one containing the | |
b12d437b | 91 | data. |
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92 | |
93 | If a drive has failed or is missing at creation time, a '-' can be | |
94 | given for both the metadata and data drives for a given position. | |
95 | ||
96 | ||
97 | Example tables | |
98 | -------------- | |
b12d437b | 99 | # RAID4 - 4 data drives, 1 parity (no metadata devices) |
9d09e663 N |
100 | # No metadata devices specified to hold superblock/bitmap info |
101 | # Chunk size of 1MiB | |
102 | # (Lines separated for easy reading) | |
c0a2fa1e | 103 | |
9d09e663 N |
104 | 0 1960893648 raid \ |
105 | raid4 1 2048 \ | |
106 | 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81 | |
107 | ||
b12d437b | 108 | # RAID4 - 4 data drives, 1 parity (with metadata devices) |
9d09e663 N |
109 | # Chunk size of 1MiB, force RAID initialization, |
110 | # min recovery rate at 20 kiB/sec/disk | |
c0a2fa1e | 111 | |
9d09e663 | 112 | 0 1960893648 raid \ |
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113 | raid4 4 2048 sync min_recovery_rate 20 \ |
114 | 5 8:17 8:18 8:33 8:34 8:49 8:50 8:65 8:66 8:81 8:82 | |
9d09e663 | 115 | |
c0a2fa1e | 116 | 'dmsetup table' displays the table used to construct the mapping. |
46bed2b5 | 117 | The optional parameters are always printed in the order listed |
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118 | above with "sync" or "nosync" always output ahead of the other |
119 | arguments, regardless of the order used when originally loading the table. | |
46bed2b5 | 120 | Arguments that can be repeated are ordered by value. |
9d09e663 | 121 | |
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122 | 'dmsetup status' yields information on the state and health of the |
123 | array. | |
124 | The output is as follows: | |
9d09e663 N |
125 | 1: <s> <l> raid \ |
126 | 2: <raid_type> <#devices> <1 health char for each dev> <resync_ratio> | |
127 | ||
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128 | Line 1 is the standard output produced by device-mapper. |
129 | Line 2 is produced by the raid target, and best explained by example: | |
9d09e663 N |
130 | 0 1960893648 raid raid4 5 AAAAA 2/490221568 |
131 | Here we can see the RAID type is raid4, there are 5 devices - all of | |
132 | which are 'A'live, and the array is 2/490221568 complete with recovery. | |
c0a2fa1e JB |
133 | Faulty or missing devices are marked 'D'. Devices that are out-of-sync |
134 | are marked 'a'. |