dm raid: improve table parameters documentation
Add more information about some dm-raid table parameters and clarify how parameters are printed when 'dmsetup table' is issued. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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Jonathan Brassow
Alasdair G Kergon
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c0a2fa1ef1
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@ -1,49 +1,75 @@
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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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dm-raid
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-------
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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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The device-mapper RAID (dm-raid) target provides a bridge from DM to MD.
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It allows the MD RAID drivers to be accessed using a device-mapper
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interface.
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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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The target is named "raid" and it accepts the following parameters:
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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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<raid_type> <#raid_params> <raid_params> \
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<#raid_devs> <metadata_dev0> <dev0> [.. <metadata_devN> <devN>]
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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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<raid_type>:
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raid4 RAID4 dedicated parity disk
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raid5_la RAID5 left asymmetric
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- rotating parity 0 with data continuation
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raid5_ra RAID5 right asymmetric
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- rotating parity N with data continuation
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raid5_ls RAID5 left symmetric
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- rotating parity 0 with data restart
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raid5_rs RAID5 right symmetric
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- rotating parity N with data restart
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raid6_zr RAID6 zero restart
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- rotating parity zero (left-to-right) with data restart
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raid6_nr RAID6 N restart
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- rotating parity N (right-to-left) with data restart
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raid6_nc RAID6 N continue
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- rotating parity N (right-to-left) with data continuation
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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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Refererence: Chapter 4 of
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http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf
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NB. Currently all metadata devices must be specified as '-'.
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<#raid_params>: The number of parameters that follow.
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Examples:
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<raid_params> consists of
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Mandatory parameters:
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<chunk_size>: Chunk size in sectors. This parameter is often known as
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"stripe size". It is the only mandatory parameter and
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is placed first.
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followed by optional parameters (in any order):
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[sync|nosync] Force or prevent RAID initialization.
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[rebuild <idx>] Rebuild drive number idx (first drive is 0).
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[daemon_sleep <ms>]
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Interval between runs of the bitmap daemon that
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clear bits. A longer interval means less bitmap I/O but
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resyncing after a failure is likely to take longer.
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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 (higher RAIDs only)
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<#raid_devs>: The number of devices composing the array.
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Each device consists of two entries. The first is the device
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containing the metadata (if any); the second is the one containing the
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data. Currently, separate metadata devices are not supported and '-'
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is required in place of the metadata device.
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If a drive has failed or is missing at creation time, a '-' can be
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given for both the metadata and data drives for a given position.
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Example tables
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--------------
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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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@ -51,20 +77,26 @@ Examples:
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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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'dmsetup table' displays the table used to construct the mapping.
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The optional parameters will always be printed in the order listed
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above with "sync" or "nosync" always output ahead of the other
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arguments, regardless of the order used when originally loading the table.
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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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'dmsetup status' yields information on the state and health of the
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array.
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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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Line 1 is the standard output produced by device-mapper.
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Line 2 is produced by the raid target, and best explained 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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Faulty or missing devices are marked 'D'. Devices that are out-of-sync
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are marked 'a'.
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