diff options
| -rw-r--r-- | Documentation/device-mapper/dm-raid.txt | 58 |
1 files changed, 55 insertions, 3 deletions
diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt index df2d636b6088..e5b6497116f4 100644 --- a/Documentation/device-mapper/dm-raid.txt +++ b/Documentation/device-mapper/dm-raid.txt @@ -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. |