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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 2355bef14653..000000000000 --- a/Documentation/device-mapper/dm-raid.txt +++ /dev/null @@ -1,354 +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>: - raid0 RAID0 striping (no resilience) - raid1 RAID1 mirroring - raid4 RAID4 with dedicated last parity disk - raid5_n RAID5 with dedicated last parity disk supporting takeover - Same as raid4 - -Transitory layout - 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 - raid6_n_6 RAID6 with dedicate parity disks - - parity and Q-syndrome on the last 2 disks; - layout for takeover from/to raid4/raid5_n - raid6_la_6 Same as "raid_la" plus dedicated last Q-syndrome disk - - layout for takeover from raid5_la from/to raid6 - raid6_ra_6 Same as "raid5_ra" dedicated last Q-syndrome disk - - layout for takeover from raid5_ra from/to raid6 - raid6_ls_6 Same as "raid5_ls" dedicated last Q-syndrome disk - - layout for takeover from raid5_ls from/to raid6 - raid6_rs_6 Same as "raid5_rs" dedicated last Q-syndrome disk - - layout for takeover from raid5_rs from/to raid6 - raid10 Various RAID10 inspired algorithms chosen by additional params - (see raid10_format and raid10_copies below) - - 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'. - - [delta_disks <N>] - The delta_disks option value (-251 < N < +251) triggers - device removal (negative value) or device addition (positive - value) to any reshape supporting raid levels 4/5/6 and 10. - RAID levels 4/5/6 allow for addition of devices (metadata - and data device tuple), raid10_near and raid10_offset only - allow for device addition. raid10_far does not support any - reshaping at all. - A minimum of devices have to be kept to enforce resilience, - which is 3 devices for raid4/5 and 4 devices for raid6. - - [data_offset <sectors>] - This option value defines the offset into each data device - where the data starts. This is used to provide out-of-place - reshaping space to avoid writing over data while - changing the layout of stripes, hence an interruption/crash - may happen at any time without the risk of losing data. - E.g. when adding devices to an existing raid set during - forward reshaping, the out-of-place space will be allocated - at the beginning of each raid device. The kernel raid4/5/6/10 - MD personalities supporting such device addition will read the data from - the existing first stripes (those with smaller number of stripes) - starting at data_offset to fill up a new stripe with the larger - number of stripes, calculate the redundancy blocks (CRC/Q-syndrome) - and write that new stripe to offset 0. Same will be applied to all - N-1 other new stripes. This out-of-place scheme is used to change - the RAID type (i.e. the allocation algorithm) as well, e.g. - changing from raid5_ls to raid5_n. - - [journal_dev <dev>] - This option adds a journal device to raid4/5/6 raid sets and - uses it to close the 'write hole' caused by the non-atomic updates - to the component devices which can cause data loss during recovery. - The journal device is used as writethrough thus causing writes to - be throttled versus non-journaled raid4/5/6 sets. - Takeover/reshape is not possible with a raid4/5/6 journal device; - it has to be deconfigured before requesting these. - - [journal_mode <mode>] - This option sets the caching mode on journaled raid4/5/6 raid sets - (see 'journal_dev <dev>' above) to 'writethrough' or 'writeback'. - If 'writeback' is selected the journal device has to be resilient - and must not suffer from the 'write hole' problem itself (e.g. use - raid1 or raid10) to avoid a single point of failure. - -<#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. A Maximum of 64 metadata/data device entries are supported - up to target version 1.8.0. - 1.9.0 supports up to 253 which is enforced by the used MD kernel runtime. - - 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. - <data_offset> The current data offset to the start of the user data on - each component device of a raid set (see the respective - raid parameter to support out-of-place reshaping). - <journal_char> 'A' - active write-through journal device. - 'a' - active write-back journal device. - 'D' - dead journal device. - '-' - no journal device. - - -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. - - -Discard Support ---------------- -The implementation of discard support among hardware vendors varies. -When a block is discarded, some storage devices will return zeroes when -the block is read. These devices set the 'discard_zeroes_data' -attribute. Other devices will return random data. Confusingly, some -devices that advertise 'discard_zeroes_data' will not reliably return -zeroes when discarded blocks are read! Since RAID 4/5/6 uses blocks -from a number of devices to calculate parity blocks and (for performance -reasons) relies on 'discard_zeroes_data' being reliable, it is important -that the devices be consistent. Blocks may be discarded in the middle -of a RAID 4/5/6 stripe and if subsequent read results are not -consistent, the parity blocks may be calculated differently at any time; -making the parity blocks useless for redundancy. It is important to -understand how your hardware behaves with discards if you are going to -enable discards with RAID 4/5/6. - -Since the behavior of storage devices is unreliable in this respect, -even when reporting 'discard_zeroes_data', by default RAID 4/5/6 -discard support is disabled -- this ensures data integrity at the -expense of losing some performance. - -Storage devices that properly support 'discard_zeroes_data' are -increasingly whitelisted in the kernel and can thus be trusted. - -For trusted devices, the following dm-raid module parameter can be set -to safely enable discard support for RAID 4/5/6: - 'devices_handle_discards_safely' - - -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". -1.6.0 Add discard support (and devices_handle_discard_safely module param). -1.7.0 Add support for MD RAID0 mappings. -1.8.0 Explicitly check for compatible flags in the superblock metadata - and reject to start the raid set if any are set by a newer - target version, thus avoiding data corruption on a raid set - with a reshape in progress. -1.9.0 Add support for RAID level takeover/reshape/region size - and set size reduction. -1.9.1 Fix activation of existing RAID 4/10 mapped devices -1.9.2 Don't emit '- -' on the status table line in case the constructor - fails reading a superblock. Correctly emit 'maj:min1 maj:min2' and - 'D' on the status line. If '- -' is passed into the constructor, emit - '- -' on the table line and '-' as the status line health character. -1.10.0 Add support for raid4/5/6 journal device -1.10.1 Fix data corruption on reshape request -1.11.0 Fix table line argument order - (wrong raid10_copies/raid10_format sequence) -1.11.1 Add raid4/5/6 journal write-back support via journal_mode option -1.12.1 Fix for MD deadlock between mddev_suspend() and md_write_start() available -1.13.0 Fix dev_health status at end of "recover" (was 'a', now 'A') -1.13.1 Fix deadlock caused by early md_stop_writes(). Also fix size an - state races. -1.13.2 Fix raid redundancy validation and avoid keeping raid set frozen -1.14.0 Fix reshape race on small devices. Fix stripe adding reshape - deadlock/potential data corruption. Update superblock when - specific devices are requested via rebuild. Fix RAID leg - rebuild errors. |