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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 deleted file mode 100644 index ef8ba9fa58c4..000000000000 --- a/Documentation/device-mapper/dm-raid.txt +++ /dev/null @@ -1,226 +0,0 @@ -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. - - -Mapping Table 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 - raid10 Various RAID10 inspired algorithms chosen by additional params - - RAID10: Striped Mirrors (aka 'Striping on top of mirrors') - - RAID1E: Integrated Adjacent Stripe Mirroring - - RAID1E: Integrated Offset Stripe Mirroring - - and other similar RAID10 variants - - 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>] Mark drive index 'idx' write-mostly. - [max_write_behind <sectors>] See '--write-behind=' (man mdadm) - [stripe_cache <sectors>] Stripe cache size (RAID 4/5/6 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. - - [raid10_copies <# copies>] - [raid10_format <near|far|offset>] - These two options are used to alter the default layout of - a RAID10 configuration. The number of copies is can be - specified, but the default is 2. There are also three - variations to how the copies are laid down - the default - is "near". Near copies are what most people think of with - respect to mirroring. If these options are left unspecified, - or 'raid10_copies 2' and/or 'raid10_format near' are given, - then the layouts for 2, 3 and 4 devices are: - 2 drives 3 drives 4 drives - -------- ---------- -------------- - A1 A1 A1 A1 A2 A1 A1 A2 A2 - A2 A2 A2 A3 A3 A3 A3 A4 A4 - A3 A3 A4 A4 A5 A5 A5 A6 A6 - A4 A4 A5 A6 A6 A7 A7 A8 A8 - .. .. .. .. .. .. .. .. .. - The 2-device layout is equivalent 2-way RAID1. The 4-device - layout is what a traditional RAID10 would look like. The - 3-device layout is what might be called a 'RAID1E - Integrated - Adjacent Stripe Mirroring'. - - If 'raid10_copies 2' and 'raid10_format far', then the layouts - for 2, 3 and 4 devices are: - 2 drives 3 drives 4 drives - -------- -------------- -------------------- - A1 A2 A1 A2 A3 A1 A2 A3 A4 - A3 A4 A4 A5 A6 A5 A6 A7 A8 - A5 A6 A7 A8 A9 A9 A10 A11 A12 - .. .. .. .. .. .. .. .. .. - A2 A1 A3 A1 A2 A2 A1 A4 A3 - A4 A3 A6 A4 A5 A6 A5 A8 A7 - A6 A5 A9 A7 A8 A10 A9 A12 A11 - .. .. .. .. .. .. .. .. .. - - If 'raid10_copies 2' and 'raid10_format offset', then the - layouts for 2, 3 and 4 devices are: - 2 drives 3 drives 4 drives - -------- ------------ ----------------- - A1 A2 A1 A2 A3 A1 A2 A3 A4 - A2 A1 A3 A1 A2 A2 A1 A4 A3 - A3 A4 A4 A5 A6 A5 A6 A7 A8 - A4 A3 A6 A4 A5 A6 A5 A8 A7 - A5 A6 A7 A8 A9 A9 A10 A11 A12 - A6 A5 A9 A7 A8 A10 A9 A12 A11 - .. .. .. .. .. .. .. .. .. - Here we see layouts closely akin to 'RAID1E - Integrated - Offset Stripe Mirroring'. - -<#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 - - -Status Output -------------- -'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 (normally a single line, but expanded here for -clarity): -1: <s> <l> raid \ -2: <raid_type> <#devices> <health_chars> \ -3: <sync_ratio> <sync_action> <mismatch_cnt> - -Line 1 is the standard output produced by device-mapper. -Line 2 & 3 are produced by the raid target and are best explained by example: - 0 1960893648 raid raid4 5 AAAAA 2/490221568 init 0 -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 its initial -recovery. Here is a fuller description of the individual fields: - <raid_type> Same as the <raid_type> used to create the array. - <health_chars> One char for each device, indicating: 'A' = alive and - in-sync, 'a' = alive but not in-sync, 'D' = dead/failed. - <sync_ratio> The ratio indicating how much of the array has undergone - the process described by 'sync_action'. If the - 'sync_action' is "check" or "repair", then the process - of "resync" or "recover" can be considered complete. - <sync_action> One of the following possible states: - idle - No synchronization action is being performed. - frozen - The current action has been halted. - resync - Array is undergoing its initial synchronization - or is resynchronizing after an unclean shutdown - (possibly aided by a bitmap). - recover - A device in the array is being rebuilt or - replaced. - check - A user-initiated full check of the array is - being performed. All blocks are read and - checked for consistency. The number of - discrepancies found are recorded in - <mismatch_cnt>. No changes are made to the - array by this action. - repair - The same as "check", but discrepancies are - corrected. - reshape - The array is undergoing a reshape. - <mismatch_cnt> The number of discrepancies found between mirror copies - in RAID1/10 or wrong parity values found in RAID4/5/6. - This value is valid only after a "check" of the array - is performed. A healthy array has a 'mismatch_cnt' of 0. - -Message Interface ------------------ -The dm-raid target will accept certain actions through the 'message' interface. -('man dmsetup' for more information on the message interface.) These actions -include: - "idle" - Halt the current sync action. - "frozen" - Freeze the current sync action. - "resync" - Initiate/continue a resync. - "recover"- Initiate/continue a recover process. - "check" - Initiate a check (i.e. a "scrub") of the array. - "repair" - Initiate a repair of the array. - "reshape"- Currently unsupported (-EINVAL). - -Version History ---------------- -1.0.0 Initial version. Support for RAID 4/5/6 -1.1.0 Added support for RAID 1 -1.2.0 Handle creation of arrays that contain failed devices. -1.3.0 Added support for RAID 10 -1.3.1 Allow device replacement/rebuild for RAID 10 -1.3.2 Fix/improve redundancy checking for RAID10 -1.4.0 Non-functional change. Removes arg from mapping function. -1.4.1 RAID10 fix redundancy validation checks (commit 55ebbb5). -1.4.2 Add RAID10 "far" and "offset" algorithm support. -1.5.0 Add message interface to allow manipulation of the sync_action. - New status (STATUSTYPE_INFO) fields: sync_action and mismatch_cnt. -1.5.1 Add ability to restore transiently failed devices on resume. -1.5.2 'mismatch_cnt' is zero unless [last_]sync_action is "check". |