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DM RAID: Add code to validate replacement slots for RAID10 arrays RAID10 can handle 'copies - 1' failures for each mirror group. This code ensures the user has provided a valid array - one whose devices specified for rebuild do not exceed the amount of redundancy available. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
144 lines
5.6 KiB
Plaintext
144 lines
5.6 KiB
Plaintext
dm-raid
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-------
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The device-mapper RAID (dm-raid) target provides a bridge from DM to MD.
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It allows the MD RAID drivers to be accessed using a device-mapper
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interface.
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The target is named "raid" and it accepts the following parameters:
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<raid_type> <#raid_params> <raid_params> \
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<#raid_devs> <metadata_dev0> <dev0> [.. <metadata_devN> <devN>]
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<raid_type>:
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raid1 RAID1 mirroring
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raid4 RAID4 dedicated parity disk
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raid5_la RAID5 left asymmetric
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- rotating parity 0 with data continuation
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raid5_ra RAID5 right asymmetric
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- rotating parity N with data continuation
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raid5_ls RAID5 left symmetric
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- rotating parity 0 with data restart
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raid5_rs RAID5 right symmetric
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- rotating parity N with data restart
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raid6_zr RAID6 zero restart
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- rotating parity zero (left-to-right) with data restart
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raid6_nr RAID6 N restart
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- rotating parity N (right-to-left) with data restart
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raid6_nc RAID6 N continue
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- rotating parity N (right-to-left) with data continuation
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raid10 Various RAID10 inspired algorithms chosen by additional params
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- RAID10: Striped Mirrors (aka 'Striping on top of mirrors')
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- RAID1E: Integrated Adjacent Stripe Mirroring
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- and other similar RAID10 variants
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Reference: Chapter 4 of
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http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf
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<#raid_params>: The number of parameters that follow.
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<raid_params> consists of
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Mandatory parameters:
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<chunk_size>: Chunk size in sectors. This parameter is often known as
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"stripe size". It is the only mandatory parameter and
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is placed first.
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followed by optional parameters (in any order):
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[sync|nosync] Force or prevent RAID initialization.
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[rebuild <idx>] Rebuild drive number idx (first drive is 0).
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[daemon_sleep <ms>]
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Interval between runs of the bitmap daemon that
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clear bits. A longer interval means less bitmap I/O but
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resyncing after a failure is likely to take longer.
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[min_recovery_rate <kB/sec/disk>] Throttle RAID initialization
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[max_recovery_rate <kB/sec/disk>] Throttle RAID initialization
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[write_mostly <idx>] Drive index is write-mostly
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[max_write_behind <sectors>] See '-write-behind=' (man mdadm)
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[stripe_cache <sectors>] Stripe cache size (higher RAIDs only)
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[region_size <sectors>]
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The region_size multiplied by the number of regions is the
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logical size of the array. The bitmap records the device
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synchronisation state for each region.
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[raid10_copies <# copies>]
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[raid10_format near]
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These two options are used to alter the default layout of
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a RAID10 configuration. The number of copies is can be
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specified, but the default is 2. There are other variations
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to how the copies are laid down - the default and only current
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option is "near". Near copies are what most people think of
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with respect to mirroring. If these options are left
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unspecified, or 'raid10_copies 2' and/or 'raid10_format near'
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are given, then the layouts for 2, 3 and 4 devices are:
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2 drives 3 drives 4 drives
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-------- ---------- --------------
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A1 A1 A1 A1 A2 A1 A1 A2 A2
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A2 A2 A2 A3 A3 A3 A3 A4 A4
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A3 A3 A4 A4 A5 A5 A5 A6 A6
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A4 A4 A5 A6 A6 A7 A7 A8 A8
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.. .. .. .. .. .. .. .. ..
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The 2-device layout is equivalent 2-way RAID1. The 4-device
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layout is what a traditional RAID10 would look like. The
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3-device layout is what might be called a 'RAID1E - Integrated
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Adjacent Stripe Mirroring'.
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<#raid_devs>: The number of devices composing the array.
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Each device consists of two entries. The first is the device
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containing the metadata (if any); the second is the one containing the
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data.
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If a drive has failed or is missing at creation time, a '-' can be
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given for both the metadata and data drives for a given position.
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Example tables
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--------------
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# RAID4 - 4 data drives, 1 parity (no metadata devices)
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# No metadata devices specified to hold superblock/bitmap info
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# Chunk size of 1MiB
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# (Lines separated for easy reading)
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0 1960893648 raid \
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raid4 1 2048 \
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5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81
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# RAID4 - 4 data drives, 1 parity (with metadata devices)
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# Chunk size of 1MiB, force RAID initialization,
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# min recovery rate at 20 kiB/sec/disk
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0 1960893648 raid \
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raid4 4 2048 sync min_recovery_rate 20 \
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5 8:17 8:18 8:33 8:34 8:49 8:50 8:65 8:66 8:81 8:82
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'dmsetup table' displays the table used to construct the mapping.
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The optional parameters are always printed in the order listed
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above with "sync" or "nosync" always output ahead of the other
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arguments, regardless of the order used when originally loading the table.
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Arguments that can be repeated are ordered by value.
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'dmsetup status' yields information on the state and health of the
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array.
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The output is as follows:
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1: <s> <l> raid \
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2: <raid_type> <#devices> <1 health char for each dev> <resync_ratio>
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Line 1 is the standard output produced by device-mapper.
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Line 2 is produced by the raid target, and best explained by example:
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0 1960893648 raid raid4 5 AAAAA 2/490221568
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Here we can see the RAID type is raid4, there are 5 devices - all of
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which are 'A'live, and the array is 2/490221568 complete with recovery.
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Faulty or missing devices are marked 'D'. Devices that are out-of-sync
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are marked 'a'.
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Version History
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---------------
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1.0.0 Initial version. Support for RAID 4/5/6
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1.1.0 Added support for RAID 1
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1.2.0 Handle creation of arrays that contain failed devices.
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1.3.0 Added support for RAID 10
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1.3.1 Allow device replacement/rebuild for RAID 10
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