Commit d41bfed0 authored by Heinz Mauelshagen's avatar Heinz Mauelshagen Committed by Mike Snitzer

dm raid: update Documentation about reshaping/takeover/additonal RAID types

Signed-off-by: default avatarHeinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 9dbd1aa3
......@@ -14,8 +14,12 @@ The target is named "raid" and it accepts the following parameters:
<#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 @@ The target is named "raid" and it accepts the following parameters:
- 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 @@ The target is named "raid" and it accepts the following parameters:
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 @@ include:
"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 @@ Version History
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.
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment