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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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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,70 +1,102 @@ | ||
| 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> | ||
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||
| 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". | ||
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||
| 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 | ||
|
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||
| 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. | ||
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||
| NB. Currently all metadata devices must be specified as '-'. | ||
|
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||
| Examples: | ||
| The target is named "raid" and it accepts the following parameters: | ||
|
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| <raid_type> <#raid_params> <raid_params> \ | ||
| <#raid_devs> <metadata_dev0> <dev0> [.. <metadata_devN> <devN>] | ||
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||
| <raid_type>: | ||
| 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 | ||
|
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||
| Refererence: Chapter 4 of | ||
| http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf | ||
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| <#raid_params>: The number of parameters that follow. | ||
|
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||
| <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. | ||
|
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||
| [rebuild <idx>] Rebuild drive number idx (first drive is 0). | ||
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||
| [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. | ||
|
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||
| [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 (higher RAIDs only) | ||
|
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||
| <#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. | ||
|
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||
| 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. | ||
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| 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) | ||
|
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||
| 0 1960893648 raid \ | ||
| raid4 1 2048 \ | ||
| 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81 | ||
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| # RAID4 - 4 data drives, 1 parity (no metadata devices) | ||
| # Chunk size of 1MiB, force RAID initialization, | ||
| # min recovery rate at 20 kiB/sec/disk | ||
|
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||
| 0 1960893648 raid \ | ||
| raid4 4 2048 min_recovery_rate 20 sync\ | ||
| 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 | ||
| 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. | ||
|
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||
| 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> | ||
|
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||
| 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'. |