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Diffstat (limited to 'Documentation/device-mapper/dm-raid.txt')
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diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt new file mode 100644 index 00000000..946c7334 --- /dev/null +++ b/Documentation/device-mapper/dm-raid.txt @@ -0,0 +1,108 @@ +dm-raid +------- + +The device-mapper RAID (dm-raid) target provides a bridge from DM to MD. +It allows the MD RAID drivers to be accessed using a device-mapper +interface. + +The target is named "raid" and it accepts the following parameters: + + <raid_type> <#raid_params> <raid_params> \ + <#raid_devs> <metadata_dev0> <dev0> [.. <metadata_devN> <devN>] + +<raid_type>: + raid1 RAID1 mirroring + raid4 RAID4 dedicated parity disk + raid5_la RAID5 left asymmetric + - rotating parity 0 with data continuation + raid5_ra RAID5 right asymmetric + - rotating parity N with data continuation + raid5_ls RAID5 left symmetric + - rotating parity 0 with data restart + raid5_rs RAID5 right symmetric + - rotating parity N with data restart + raid6_zr RAID6 zero restart + - rotating parity zero (left-to-right) with data restart + raid6_nr RAID6 N restart + - rotating parity N (right-to-left) with data restart + raid6_nc RAID6 N continue + - rotating parity N (right-to-left) with data continuation + + Reference: Chapter 4 of + http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf + +<#raid_params>: The number of parameters that follow. + +<raid_params> consists of + Mandatory parameters: + <chunk_size>: Chunk size in sectors. This parameter is often known as + "stripe size". It is the only mandatory parameter and + is placed first. + + followed by optional parameters (in any order): + [sync|nosync] Force or prevent RAID initialization. + + [rebuild <idx>] Rebuild drive number idx (first drive is 0). + + [daemon_sleep <ms>] + Interval between runs of the bitmap daemon that + clear bits. A longer interval means less bitmap I/O but + resyncing after a failure is likely to take longer. + + [min_recovery_rate <kB/sec/disk>] Throttle RAID initialization + [max_recovery_rate <kB/sec/disk>] Throttle RAID initialization + [write_mostly <idx>] Drive index is write-mostly + [max_write_behind <sectors>] See '-write-behind=' (man mdadm) + [stripe_cache <sectors>] Stripe cache size (higher RAIDs only) + [region_size <sectors>] + The region_size multiplied by the number of regions is the + logical size of the array. The bitmap records the device + synchronisation state for each region. + +<#raid_devs>: The number of devices composing the array. + Each device consists of two entries. The first is the device + containing the metadata (if any); the second is the one containing the + data. + + If a drive has failed or is missing at creation time, a '-' can be + given for both the metadata and data drives for a given position. + + +Example tables +-------------- +# RAID4 - 4 data drives, 1 parity (no metadata devices) +# No metadata devices specified to hold superblock/bitmap info +# Chunk size of 1MiB +# (Lines separated for easy reading) + +0 1960893648 raid \ + raid4 1 2048 \ + 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81 + +# RAID4 - 4 data drives, 1 parity (with metadata devices) +# Chunk size of 1MiB, force RAID initialization, +# min recovery rate at 20 kiB/sec/disk + +0 1960893648 raid \ + raid4 4 2048 sync min_recovery_rate 20 \ + 5 8:17 8:18 8:33 8:34 8:49 8:50 8:65 8:66 8:81 8:82 + +'dmsetup table' displays the table used to construct the mapping. +The optional parameters are always printed in the order listed +above with "sync" or "nosync" always output ahead of the other +arguments, regardless of the order used when originally loading the table. +Arguments that can be repeated are ordered by value. + +'dmsetup status' yields information on the state and health of the +array. +The output is as follows: +1: <s> <l> raid \ +2: <raid_type> <#devices> <1 health char for each dev> <resync_ratio> + +Line 1 is the standard output produced by device-mapper. +Line 2 is produced by the raid target, and best explained by example: + 0 1960893648 raid raid4 5 AAAAA 2/490221568 +Here we can see the RAID type is raid4, there are 5 devices - all of +which are 'A'live, and the array is 2/490221568 complete with recovery. +Faulty or missing devices are marked 'D'. Devices that are out-of-sync +are marked 'a'. |