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