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-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'.