diff options
Diffstat (limited to 'Documentation/device-mapper')
| -rw-r--r-- | Documentation/device-mapper/dm-raid.txt | 58 | ||||
| -rw-r--r-- | Documentation/device-mapper/log-writes.txt | 10 |
2 files changed, 60 insertions, 8 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. diff --git a/Documentation/device-mapper/log-writes.txt b/Documentation/device-mapper/log-writes.txt index c10f30c9b534..f4ebcbaf50f3 100644 --- a/Documentation/device-mapper/log-writes.txt +++ b/Documentation/device-mapper/log-writes.txt @@ -14,14 +14,14 @@ Log Ordering We log things in order of completion once we are sure the write is no longer in cache. This means that normal WRITE requests are not actually logged until the -next REQ_FLUSH request. This is to make it easier for userspace to replay the -log in a way that correlates to what is on disk and not what is in cache, to -make it easier to detect improper waiting/flushing. +next REQ_PREFLUSH request. This is to make it easier for userspace to replay +the log in a way that correlates to what is on disk and not what is in cache, +to make it easier to detect improper waiting/flushing. This works by attaching all WRITE requests to a list once the write completes. -Once we see a REQ_FLUSH request we splice this list onto the request and once +Once we see a REQ_PREFLUSH request we splice this list onto the request and once the FLUSH request completes we log all of the WRITEs and then the FLUSH. Only -completed WRITEs, at the time the REQ_FLUSH is issued, are added in order to +completed WRITEs, at the time the REQ_PREFLUSH is issued, are added in order to simulate the worst case scenario with regard to power failures. Consider the following example (W means write, C means complete): |