-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.
+dm-raid
+-------
-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:
+The device-mapper RAID (dm-raid) target provides a bridge from DM to MD.
+It allows the MD RAID drivers to be accessed using a device-mapper
+interface.
-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
+The target is named "raid" and it accepts the following parameters:
+
+ <raid_type> <#raid_params> <raid_params> \
+ <#raid_devs> <metadata_dev0> <dev0> [.. <metadata_devN> <devN>]
+
+<raid_type>:
+ raid1 RAID1 mirroring
+ raid4 RAID4 dedicated parity disk
+ raid5_la RAID5 left asymmetric
+ - rotating parity 0 with data continuation
+ raid5_ra RAID5 right asymmetric
+ - rotating parity N with data continuation
+ raid5_ls RAID5 left symmetric
+ - rotating parity 0 with data restart
+ raid5_rs RAID5 right symmetric
+ - rotating parity N with data restart
+ raid6_zr RAID6 zero restart
+ - rotating parity zero (left-to-right) with data restart
+ raid6_nr RAID6 N restart
+ - rotating parity N (right-to-left) with data restart
+ raid6_nc RAID6 N continue
+ - rotating parity N (right-to-left) with data continuation
+
+ Refererence: Chapter 4 of
+ http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf
+
+<#raid_params>: The number of parameters that follow.
+
+<raid_params> consists of
+ Mandatory parameters:
+ <chunk_size>: Chunk size in sectors. This parameter is often known as
+ "stripe size". It is the only mandatory parameter and
+ is placed first.
+
+ followed by optional parameters (in any order):
+ [sync|nosync] Force or prevent RAID initialization.
+
+ [rebuild <idx>] Rebuild drive number idx (first drive is 0).
+
+ [daemon_sleep <ms>]
+ Interval between runs of the bitmap daemon that
+ clear bits. A longer interval means less bitmap I/O but
+ resyncing after a failure is likely to take longer.
+
+ [min_recovery_rate <kB/sec/disk>] Throttle RAID initialization
+ [max_recovery_rate <kB/sec/disk>] Throttle RAID initialization
+ [write_mostly <idx>] Drive index is write-mostly
+ [max_write_behind <sectors>] See '-write-behind=' (man mdadm)
+ [stripe_cache <sectors>] Stripe cache size (higher RAIDs only)
+ [region_size <sectors>]
+ The region_size multiplied by the number of regions is the
+ logical size of the array. The bitmap records the device
+ synchronisation state for each region.
+
+<#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.
+
+ 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.
+
+
+Example tables
+--------------
+# RAID4 - 4 data drives, 1 parity (no metadata devices)
# 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)
+# RAID4 - 4 data drives, 1 parity (with 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
+ raid4 4 2048 sync min_recovery_rate 20 \
+ 5 8:17 8:18 8:33 8:34 8:49 8:50 8:65 8:66 8:81 8:82
-Performing a 'dmsetup table' should display the CTR table used to
-construct the mapping (with possible reordering of optional
-parameters).
+'dmsetup table' displays the table used to construct the mapping.
+The optional parameters are always printed in the order listed
+above with "sync" or "nosync" always output ahead of the other
+arguments, regardless of the order used when originally loading the table.
+Arguments that can be repeated are ordered by value.
-Performing a 'dmsetup status' will yield information on the state and
-health of the array. The output is as follows:
+'dmsetup status' yields 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:
+Line 1 is the standard output produced by device-mapper.
+Line 2 is produced by the raid target, and best explained 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.
+Faulty or missing devices are marked 'D'. Devices that are out-of-sync
+are marked 'a'.
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