diff options
Diffstat (limited to 'Documentation/device-mapper/dm-raid.txt')
| -rw-r--r-- | Documentation/device-mapper/dm-raid.txt | 92 |
1 files changed, 89 insertions, 3 deletions
diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt index df2d636b6088..7e06e65586d4 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 supporting 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; + layout 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 +132,57 @@ 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 tuple), raid10_near and raid10_offset only + allow for device addition. 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. + + [journal_dev <dev>] + This option adds a journal device to raid4/5/6 raid sets and + uses it to close the 'write hole' caused by the non-atomic updates + to the component devices which can cause data loss during recovery. + The journal device is used as writethrough thus causing writes to + be throttled versus non-journaled raid4/5/6 sets. + Takeover/reshape is not possible with a raid4/5/6 journal device; + it has to be deconfigured before requesting these. + + [journal_mode <mode>] + This option sets the caching mode on journaled raid4/5/6 raid sets + (see 'journal_dev <dev>' above) to 'writethrough' or 'writeback'. + If 'writeback' is selected the journal device has to be resilient + and must not suffer from the 'write hole' problem itself (e.g. use + raid1 or raid10) to avoid a single point of failure. + <#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. @@ -195,6 +258,14 @@ recovery. Here is a fuller description of the individual fields: in RAID1/10 or wrong parity values found in RAID4/5/6. This value is valid only after a "check" of the array is performed. A healthy array has a 'mismatch_cnt' of 0. + <data_offset> The current data offset to the start of the user data on + each component device of a raid set (see the respective + raid parameter to support out-of-place reshaping). + <journal_char> 'A' - active write-through journal device. + 'a' - active write-back journal device. + 'D' - dead journal device. + '-' - no journal device. + Message Interface ----------------- @@ -207,7 +278,6 @@ 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 +327,19 @@ 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 Explicitly 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. +1.9.1 Fix activation of existing RAID 4/10 mapped devices +1.9.2 Don't emit '- -' on the status table line in case the constructor + fails reading a superblock. Correctly emit 'maj:min1 maj:min2' and + 'D' on the status line. If '- -' is passed into the constructor, emit + '- -' on the table line and '-' as the status line health character. +1.10.0 Add support for raid4/5/6 journal device +1.10.1 Fix data corruption on reshape request +1.11.0 Fix table line argument order + (wrong raid10_copies/raid10_format sequence) +1.11.1 Add raid4/5/6 journal write-back support via journal_mode option |