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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/device-mapper/dm-raid.txt | 70 |
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diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt new file mode 100644 index 00000000000..33b6b7071ac --- /dev/null +++ b/Documentation/device-mapper/dm-raid.txt @@ -0,0 +1,70 @@ +Device-mapper RAID (dm-raid) is a bridge from DM to MD. It +provides a way to use device-mapper interfaces to access the MD RAID +drivers. + +As with all device-mapper targets, the nominal public interfaces are the +constructor (CTR) tables and the status outputs (both STATUSTYPE_INFO +and STATUSTYPE_TABLE). The CTR table looks like the following: + +1: <s> <l> raid \ +2: <raid_type> <#raid_params> <raid_params> \ +3: <#raid_devs> <meta_dev1> <dev1> .. <meta_devN> <devN> + +Line 1 contains the standard first three arguments to any device-mapper +target - the start, length, and target type fields. The target type in +this case is "raid". + +Line 2 contains the arguments that define the particular raid +type/personality/level, the required arguments for that raid type, and +any optional arguments. Possible raid types include: raid4, raid5_la, +raid5_ls, raid5_rs, raid6_zr, raid6_nr, and raid6_nc. (raid1 is +planned for the future.) The list of required and optional parameters +is the same for all the current raid types. The required parameters are +positional, while the optional parameters are given as key/value pairs. +The possible parameters are as follows: + <chunk_size> Chunk size in sectors. + [[no]sync] Force/Prevent RAID initialization + [rebuild <idx>] Rebuild the drive indicated by the index + [daemon_sleep <ms>] Time between bitmap daemon work to clear bits + [min_recovery_rate <kB/sec/disk>] Throttle RAID initialization + [max_recovery_rate <kB/sec/disk>] Throttle RAID initialization + [max_write_behind <sectors>] See '-write-behind=' (man mdadm) + [stripe_cache <sectors>] Stripe cache size for higher RAIDs + +Line 3 contains the list of devices that compose the array in +metadata/data device pairs. If the metadata is stored separately, a '-' +is given for the metadata device position. 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. + +NB. Currently all metadata devices must be specified as '-'. + +Examples: +# RAID4 - 4 data drives, 1 parity +# No metadata devices specified to hold superblock/bitmap info +# Chunk size of 1MiB +# (Lines separated for easy reading) +0 1960893648 raid \ + raid4 1 2048 \ + 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81 + +# RAID4 - 4 data drives, 1 parity (no metadata devices) +# Chunk size of 1MiB, force RAID initialization, +# min recovery rate at 20 kiB/sec/disk +0 1960893648 raid \ + raid4 4 2048 min_recovery_rate 20 sync\ + 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81 + +Performing a 'dmsetup table' should display the CTR table used to +construct the mapping (with possible reordering of optional +parameters). + +Performing a 'dmsetup status' will yield information on the state and +health of the array. The output is as follows: +1: <s> <l> raid \ +2: <raid_type> <#devices> <1 health char for each dev> <resync_ratio> + +Line 1 is standard DM output. Line 2 is best shown by example: + 0 1960893648 raid raid4 5 AAAAA 2/490221568 +Here we can see the RAID type is raid4, there are 5 devices - all of +which are 'A'live, and the array is 2/490221568 complete with recovery. |