dm raid: update Documentation about reshaping/takeover/additonal RAID types
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt
index df2d636..e5b6497 100644
--- a/Documentation/device-mapper/dm-raid.txt
+++ b/Documentation/device-mapper/dm-raid.txt
@@ -14,8 +14,12 @@
<#raid_devs> <metadata_dev0> <dev0> [.. <metadata_devN> <devN>]
<raid_type>:
+ raid0 RAID0 striping (no resilience)
raid1 RAID1 mirroring
- raid4 RAID4 dedicated parity disk
+ raid4 RAID4 with dedicated last parity disk
+ raid5_n RAID5 with dedicated last parity disk suporting takeover
+ Same as raid4
+ -Transitory layout
raid5_la RAID5 left asymmetric
- rotating parity 0 with data continuation
raid5_ra RAID5 right asymmetric
@@ -30,7 +34,19 @@
- 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;
+ laylout 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
@@ -116,10 +132,41 @@
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 tupel), raid10_near and raid10_offset only
+ allow for device addtion. 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 whilst
+ 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.
+
<#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.
+ 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.
@@ -207,7 +254,6 @@
"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).
Discard Support
@@ -257,3 +303,9 @@
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 Explictely 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.