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DM RAID: Add support for MD's RAID10 "far" and "offset" algorithms Until now, dm-raid.c only supported the "near" algorthm of MD's RAID10 implementation. This patch adds support for the "far" and "offset" algorithms, but only with the improved redundancy that is brought with the introduction of the 'use_far_sets' bit, which shifts copied stripes according to smaller sets vs the entire array. That is, the 17th bit of the 'layout' variable that defines the RAID10 implementation will always be set. (More information on how the 'layout' variable selects the RAID10 algorithm can be found in the opening comments of drivers/md/raid10.c.) Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: NeilBrown <neilb@suse.de>
175 lines
7.1 KiB
Plaintext
175 lines
7.1 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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- RAID1E: Integrated Offset 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|far|offset>]
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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 also three
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variations to how the copies are laid down - the default
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is "near". Near copies are what most people think of with
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respect to mirroring. If these options are left unspecified,
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or 'raid10_copies 2' and/or 'raid10_format near' are given,
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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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If 'raid10_copies 2' and 'raid10_format far', then the layouts
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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 A2 A1 A2 A3 A1 A2 A3 A4
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A3 A4 A4 A5 A6 A5 A6 A7 A8
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A5 A6 A7 A8 A9 A9 A10 A11 A12
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.. .. .. .. .. .. .. .. ..
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A2 A1 A3 A1 A2 A2 A1 A4 A3
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A4 A3 A6 A4 A5 A6 A5 A8 A7
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A6 A5 A9 A7 A8 A10 A9 A12 A11
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.. .. .. .. .. .. .. .. ..
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If 'raid10_copies 2' and 'raid10_format offset', then the
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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 A2 A1 A2 A3 A1 A2 A3 A4
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A2 A1 A3 A1 A2 A2 A1 A4 A3
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A3 A4 A4 A5 A6 A5 A6 A7 A8
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A4 A3 A6 A4 A5 A6 A5 A8 A7
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A5 A6 A7 A8 A9 A9 A10 A11 A12
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A6 A5 A9 A7 A8 A10 A9 A12 A11
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.. .. .. .. .. .. .. .. ..
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Here we see layouts closely akin to 'RAID1E - Integrated
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Offset 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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1.3.2 Fix/improve redundancy checking for RAID10
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1.4.0 Non-functional change. Removes arg from mapping function.
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1.4.1 Add RAID10 "far" and "offset" algorithm support.
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