admin-guide/device-mapper/dm-raid.rst

5 The device-mapper RAID (dm-raid) target provides a bridge from DM to MD.
6 It allows the MD RAID drivers to be accessed using a device-mapper
95 		clear bits.  A longer interval means less bitmap I/O but
96 		resyncing after a failure is likely to take longer.
107 		Stripe cache size (RAID 4/5/6 only)
115 		a RAID10 configuration.  The number of copies is can be
134 		layout is what a traditional RAID10 would look like.  The
135 		3-device layout is what might be called a 'RAID1E - Integrated
175 		value) to any reshape supporting raid levels 4/5/6 and 10.
176 		RAID levels 4/5/6 allow for addition of devices (metadata
180 		A minimum of devices have to be kept to enforce resilience,
181 		which is 3 devices for raid4/5 and 4 devices for raid6.
191 		at the beginning of each raid device. The kernel raid4/5/6/10
194 		starting at data_offset to fill up a new stripe with the larger
202 		This option adds a journal device to raid4/5/6 raid sets and
206 		be throttled versus non-journaled raid4/5/6 sets.
207 		Takeover/reshape is not possible with a raid4/5/6 journal device;
211 		This option sets the caching mode on journaled raid4/5/6 raid sets
215 		raid1 or raid10) to avoid a single point of failure.
220 	data. A Maximum of 64 metadata/data device entries are supported
224 	If a drive has failed or is missing at creation time, a '-' can be
225 	given for both the metadata and data drives for a given position.
240           5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81
248           5 8:17 8:18 8:33 8:34 8:49 8:50 8:65 8:66 8:81 8:82
261 The output is as follows (normally a single line, but expanded here for
272         0 1960893648 raid raid4 5 AAAAA 2/490221568 init 0
274 Here we can see the RAID type is raid4, there are 5 devices - all of
275 which are 'A'live, and the array is 2/490221568 complete with its initial
276 recovery.  Here is a fuller description of the individual fields:
282 			- 'A' = alive and in-sync
283 			- 'a' = alive but not in-sync
298 				  (possibly aided by a bitmap).
300 				- A device in the array is being rebuilt or
303 				- A user-initiated full check of the array is
313 				- The array is undergoing a reshape.
315 			in RAID1/10 or wrong parity values found in RAID4/5/6.
316 			This value is valid only after a "check" of the array
317 			is performed.  A healthy array has a 'mismatch_cnt' of 0.
319 			each component device of a raid set (see the respective
321 	<journal_char>	- 'A' - active write-through journal device.
322 			- 'a' - active write-back journal device.
337 	"resync"  Initiate/continue a resync.
338 	"recover" Initiate/continue a recover process.
339 	"check"   Initiate a check (i.e. a "scrub") of the array.
340 	"repair"  Initiate a repair of the array.
347 When a block is discarded, some storage devices will return zeroes when
351 zeroes when discarded blocks are read!  Since RAID 4/5/6 uses blocks
352 from a number of devices to calculate parity blocks and (for performance
355 of a RAID 4/5/6 stripe and if subsequent read results are not
359 enable discards with RAID 4/5/6.
362 even when reporting 'discard_zeroes_data', by default RAID 4/5/6
370 to safely enable discard support for RAID 4/5/6:
380  1.0.0	Initial version.  Support for RAID 4/5/6
396 	and reject to start the raid set if any are set by a newer
397 	target version, thus avoiding data corruption on a raid set
398 	with a reshape in progress.
403 	fails reading a superblock. Correctly emit 'maj:min1 maj:min2' and
406  1.10.0	Add support for raid4/5/6 journal device
410  1.11.1	Add raid4/5/6 journal write-back support via journal_mode option
412  1.13.0	Fix dev_health status at end of "recover" (was 'a', now 'A')