Will Mdadm Automatically Use Spare

The following article looks at the Recovery and Resync operations of the Linux Software RAID tools mdadm more closely. Here nosotros will show you a few commands and explain the steps.

Perform Rebuild/Recovery

The following attributes utilise to a rebuild:^[i]

fill a new disc with relevant information from an existing array
nether the assumption that all data must be rewritten and that the information from the existing array is right
is performed when a disk has been replaced

Force Manual Recovery

Intentionally Set up Faulty Partition

root@ubuntumdraidtest:~# mdadm --manage --set-faulty /dev/mdN /dev/sdX1 mdadm: fix /dev/sdX1 faulty in /dev/mdN

Condition of Software RAIDs

root@ubuntumdraidtest:~# mdadm -D /dev/mdN provides the following overview:

/dev/md0:         Version : one.2   Creation Time : Mon Sep 30 14:59:51 2013      Raid Level : raid1      Array Size : 2095040 (2046.28 MiB 2145.32 MB)   Used Dev Size : 2095040 (2046.28 MiB 2145.32 MB)    Raid Devices : 2   Full Devices : 2     Persistence : Superblock is persistent      Update Time : Mon Oct  7 08:xi:41 2013           State : make clean, degraded   Agile Devices : one Working Devices : i  Failed Devices : one   Spare Devices : 0             Proper name : ubuntumdraidtest:0  (local to host ubuntumdraidtest)            UUID : ebe7bfba:a20bf402:f7954545:d920460f          Events : 471      Number   Major   Minor   RaidDevice State        3       8       17        0      active sync   /dev/sdb1        1       0        0        1      removed         2       8       33        -      faulty spare   /dev/sdc1

Hither the sdc1 partitioning of the RAID was set to md0 faulty and is now displayed every bit faulty spare. The status of the RAIDs changed from clean to clean, degraded.

SDX1 hot remove

root@ubuntumdraidtest:~# mdadm --manage /dev/mdN -r /dev/sdX1 mdadm: hot removed /dev/sdX1 from /dev/mdN

SDX1 add

root@ubuntumdraidtest:~# mdadm --manage /dev/mdN -a /dev/sdX1 mdadm: added /dev/sdX1

Visualization

cat /proc/mdstat shows:

md0 : active raid1 sdc1[2] sdb1[3]       2095040 blocks super ane.2 [2/1] [U_]       [>....................]  recovery =  0.4% (9600/2095040) end=3.6min spe ed=9600K/sec  unused devices: <none>

nmon shows that from /dev/sdb reads and is written /dev/sdc.

┌nmon─13g──────[H for help]───Hostname=ubuntumdraidtRefresh= 2secs ───15:08.05─┐ │ Disk I/O ──/proc/diskstats────mostly in KB/south─────Alert:contains duplicates─│ │DiskName Busy  Read WriteMB|0          |25         |50          |75       100|│ │sda        0%    0.0    0.0|        >                                        |│ │sda1       0%    0.0    0.0|>                                                |│ │sda2       0%    0.0    0.0|>disk busy not available                         |│ │sda5       0%    0.0    0.0| >                                               |│ │sdb        v%   66.iii    0.0|RRR             >                                |│ │sdb1       6%   66.iii    0.0|RRR             >                                |│ │sdc       72%    0.0   65.3|WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW             >│ │sdc1      72%    0.0   65.iii|WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW             >│ │sdd        0%    0.0    0.0|>                                                |│ │sdd1       0%    0.0    0.0|>deejay busy not available                         |│ │dm-0       0%    0.0    0.0|        >                                        |│ │dm-1       0%    0.0    0.0|>                                                |│ │md0        0%    0.0    0.0|>disk busy not available                         |│ │Totals Read-MB/s=132.half dozen    Writes-MB/s=130.7    Transfers/sec=541.7            │ │──────────────────────────────────────────────────────────────────────────────│

Behavior when using a spare disk

If a RAID is operated with a spare disk, it will jump in for the disk set to faulty. A rebuild is performed automatically. The disk ready to faulty appears in the output of mdadm -D /dev/mdN every bit faulty spare.

To put it dorsum into the assortment as a spare disk, it must start be removed using mdadm --manage /dev/mdN -r /dev/sdX1 and so added again mdadm --manage /dev/mdN -a /dev/sdd1.

Resync

The following backdrop apply to a resync:^[1]

Ensures that all data in the array is synchronized respectively consistent.
Assumption that the data is (should exist) in gild.
In case of an error while reading a device, the data is written from another device to all others.

Force Manual Resync

End Array

root@ubuntumdraidtest:~# mdadm --cease /dev/mdN mdadm: stopped /dev/mdN

Perform Resync

root@ubuntumdraidtest:~# mdadm --assemble --run --force --update=resync /dev/mdN /dev/sdX1 /dev/sdX1 mdadm: /dev/mdN has been started with 2 drives.

For further information meet:^[2]
For a list of commands, see /usr/share/medico-base/mdadm-readme-recipes.

Visualization

cat /proc/mdstat liefert:

Every two.0s: cat /proc/mdstat                                                      Wed Sep 25 15:19:59 2013  Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid1 sdb1[0] sdc1[i]      2095040 blocks super i.ii [two/2] [UU]      	[===>.................]  resync = 19.vii% (414656/2095040) terminate=0.2min speed=138218K/sec  unused devices: <none>

References

↑ ^1.0 ^ane.1 Linux RAID Wiki recovery and resync (raid.wiki.kernel.org)
↑ Resync auf einem Software-RAID erzwingen (web.archive.org)

Author: Thomas Niedermeier

Thomas Niedermeier, working in the Noesis Transfer team at Thomas-Krenn, completed his bachelor's degree in business concern informatics at the Deggendorf University of Applied Sciences. Thomas has been working for Thomas-Krenn since 2013 and is mainly responsible for the maintenance of the Thomas-Krenn wiki.