Documentation / device-mapper / dm-raid.txt
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Based on kernel version 3.9. Page generated on 2013-05-02 22:56 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 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 - RAID1E: Integrated Offset Stripe Mirroring 34 - and other similar RAID10 variants 35 36 Reference: Chapter 4 of 37 http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf 38 39 <#raid_params>: The number of parameters that follow. 40 41 <raid_params> consists of 42 Mandatory parameters: 43 <chunk_size>: Chunk size in sectors. This parameter is often known as 44 "stripe size". It is the only mandatory parameter and 45 is placed first. 46 47 followed by optional parameters (in any order): 48 [sync|nosync] Force or prevent RAID initialization. 49 50 [rebuild <idx>] Rebuild drive number idx (first drive is 0). 51 52 [daemon_sleep <ms>] 53 Interval between runs of the bitmap daemon that 54 clear bits. A longer interval means less bitmap I/O but 55 resyncing after a failure is likely to take longer. 56 57 [min_recovery_rate <kB/sec/disk>] Throttle RAID initialization 58 [max_recovery_rate <kB/sec/disk>] Throttle RAID initialization 59 [write_mostly <idx>] Drive index is write-mostly 60 [max_write_behind <sectors>] See '-write-behind=' (man mdadm) 61 [stripe_cache <sectors>] Stripe cache size (higher RAIDs only) 62 [region_size <sectors>] 63 The region_size multiplied by the number of regions is the 64 logical size of the array. The bitmap records the device 65 synchronisation state for each region. 66 67 [raid10_copies <# copies>] 68 [raid10_format <near|far|offset>] 69 These two options are used to alter the default layout of 70 a RAID10 configuration. The number of copies is can be 71 specified, but the default is 2. There are also three 72 variations to how the copies are laid down - the default 73 is "near". Near copies are what most people think of with 74 respect to mirroring. If these options are left unspecified, 75 or 'raid10_copies 2' and/or 'raid10_format near' are given, 76 then the layouts for 2, 3 and 4 devices are: 77 2 drives 3 drives 4 drives 78 -------- ---------- -------------- 79 A1 A1 A1 A1 A2 A1 A1 A2 A2 80 A2 A2 A2 A3 A3 A3 A3 A4 A4 81 A3 A3 A4 A4 A5 A5 A5 A6 A6 82 A4 A4 A5 A6 A6 A7 A7 A8 A8 83 .. .. .. .. .. .. .. .. .. 84 The 2-device layout is equivalent 2-way RAID1. The 4-device 85 layout is what a traditional RAID10 would look like. The 86 3-device layout is what might be called a 'RAID1E - Integrated 87 Adjacent Stripe Mirroring'. 88 89 If 'raid10_copies 2' and 'raid10_format far', then the layouts 90 for 2, 3 and 4 devices are: 91 2 drives 3 drives 4 drives 92 -------- -------------- -------------------- 93 A1 A2 A1 A2 A3 A1 A2 A3 A4 94 A3 A4 A4 A5 A6 A5 A6 A7 A8 95 A5 A6 A7 A8 A9 A9 A10 A11 A12 96 .. .. .. .. .. .. .. .. .. 97 A2 A1 A3 A1 A2 A2 A1 A4 A3 98 A4 A3 A6 A4 A5 A6 A5 A8 A7 99 A6 A5 A9 A7 A8 A10 A9 A12 A11 100 .. .. .. .. .. .. .. .. .. 101 102 If 'raid10_copies 2' and 'raid10_format offset', then the 103 layouts for 2, 3 and 4 devices are: 104 2 drives 3 drives 4 drives 105 -------- ------------ ----------------- 106 A1 A2 A1 A2 A3 A1 A2 A3 A4 107 A2 A1 A3 A1 A2 A2 A1 A4 A3 108 A3 A4 A4 A5 A6 A5 A6 A7 A8 109 A4 A3 A6 A4 A5 A6 A5 A8 A7 110 A5 A6 A7 A8 A9 A9 A10 A11 A12 111 A6 A5 A9 A7 A8 A10 A9 A12 A11 112 .. .. .. .. .. .. .. .. .. 113 Here we see layouts closely akin to 'RAID1E - Integrated 114 Offset Stripe Mirroring'. 115 116 <#raid_devs>: The number of devices composing the array. 117 Each device consists of two entries. The first is the device 118 containing the metadata (if any); the second is the one containing the 119 data. 120 121 If a drive has failed or is missing at creation time, a '-' can be 122 given for both the metadata and data drives for a given position. 123 124 125 Example tables 126 -------------- 127 # RAID4 - 4 data drives, 1 parity (no metadata devices) 128 # No metadata devices specified to hold superblock/bitmap info 129 # Chunk size of 1MiB 130 # (Lines separated for easy reading) 131 132 0 1960893648 raid \ 133 raid4 1 2048 \ 134 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81 135 136 # RAID4 - 4 data drives, 1 parity (with metadata devices) 137 # Chunk size of 1MiB, force RAID initialization, 138 # min recovery rate at 20 kiB/sec/disk 139 140 0 1960893648 raid \ 141 raid4 4 2048 sync min_recovery_rate 20 \ 142 5 8:17 8:18 8:33 8:34 8:49 8:50 8:65 8:66 8:81 8:82 143 144 'dmsetup table' displays the table used to construct the mapping. 145 The optional parameters are always printed in the order listed 146 above with "sync" or "nosync" always output ahead of the other 147 arguments, regardless of the order used when originally loading the table. 148 Arguments that can be repeated are ordered by value. 149 150 'dmsetup status' yields information on the state and health of the 151 array. 152 The output is as follows: 153 1: <s> <l> raid \ 154 2: <raid_type> <#devices> <1 health char for each dev> <resync_ratio> 155 156 Line 1 is the standard output produced by device-mapper. 157 Line 2 is produced by the raid target, and best explained by example: 158 0 1960893648 raid raid4 5 AAAAA 2/490221568 159 Here we can see the RAID type is raid4, there are 5 devices - all of 160 which are 'A'live, and the array is 2/490221568 complete with recovery. 161 Faulty or missing devices are marked 'D'. Devices that are out-of-sync 162 are marked 'a'. 163 164 165 Version History 166 --------------- 167 1.0.0 Initial version. Support for RAID 4/5/6 168 1.1.0 Added support for RAID 1 169 1.2.0 Handle creation of arrays that contain failed devices. 170 1.3.0 Added support for RAID 10 171 1.3.1 Allow device replacement/rebuild for RAID 10 172 1.3.2 Fix/improve redundancy checking for RAID10 173 1.4.0 Non-functional change. Removes arg from mapping function. 174 1.4.1 Add RAID10 "far" and "offset" algorithm support.
- [ device-mapper ]
- cache-policies.txt
- cache.txt
- delay.txt
- dm-crypt.txt
- dm-flakey.txt
- dm-io.txt
- dm-log.txt
- dm-queue-length.txt
- dm-raid.txt
- dm-service-time.txt
- dm-uevent.txt
- kcopyd.txt
- linear.txt
- persistent-data.txt
- snapshot.txt
- striped.txt
- thin-provisioning.txt
- verity.txt
- zero.txt
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