From c0a2fa1ef1057a1e9450d6f055f1cde2ad4f85a2 Mon Sep 17 00:00:00 2001 From: Jonathan Brassow Date: Tue, 2 Aug 2011 12:32:06 +0100 Subject: 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 Signed-off-by: Alasdair G Kergon --- Documentation/device-mapper/dm-raid.txt | 124 ++++++++++++++++++++------------ 1 file changed, 78 insertions(+), 46 deletions(-) (limited to 'Documentation') diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt index 33b6b7071ac8..4f9dd3cecc11 100644 --- a/Documentation/device-mapper/dm-raid.txt +++ b/Documentation/device-mapper/dm-raid.txt @@ -1,49 +1,75 @@ -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: raid \ -2: <#raid_params> \ -3: <#raid_devs> .. - -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 in sectors. - [[no]sync] Force/Prevent RAID initialization - [rebuild ] Rebuild the drive indicated by the index - [daemon_sleep ] Time between bitmap daemon work to clear bits - [min_recovery_rate ] Throttle RAID initialization - [max_recovery_rate ] Throttle RAID initialization - [max_write_behind ] See '-write-behind=' (man mdadm) - [stripe_cache ] 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: +The target is named "raid" and it accepts the following parameters: + + <#raid_params> \ + <#raid_devs> [.. ] + +: + 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. + + consists of + Mandatory parameters: + : 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 ] Rebuild drive number idx (first drive is 0). + + [daemon_sleep ] + 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 ] Throttle RAID initialization + [max_recovery_rate ] Throttle RAID initialization + [max_write_behind ] See '-write-behind=' (man mdadm) + [stripe_cache ] Stripe cache size (higher RAIDs only) + +<#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. Currently, separate metadata devices are not supported and '-' + is required in place of the metadata device. + + 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 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 @@ -51,20 +77,26 @@ Examples: # 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). +'dmsetup table' displays the table used to construct the mapping. +The optional parameters will always be 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. -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: raid \ 2: <#devices> <1 health char for each dev> -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'. -- cgit v1.2.3