summaryrefslogtreecommitdiff
path: root/Documentation/device-mapper
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/device-mapper')
-rw-r--r--Documentation/device-mapper/dm-raid.txt70
1 files changed, 70 insertions, 0 deletions
diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt
new file mode 100644
index 000000000000..33b6b7071ac8
--- /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.