How to "fail" a disk in md:
# mdadm /dev/mdX -f /dev/[hs]dX
How to remove a disk from md array:
# mdadm /dev/mdX -r /dev/[hs]dX
How to add a disk in md array:
This command is used also to re-add a disk back into the array if was previously removed due to disk issues.
# mdadm /dev/mdX -a /dev/[hs]dX
How to refresh the mdadm configuration file:
# mdadm --examine --scan
# echo 'DEVICE disk' > /etc/mdadm.conf
# mdadm --detail --scan >> /etc/mdadm.conf
How to display the status of md:
# mdadm --detail /dev/mdX
How to create a mirror raid device with two active devices and no spare:
# mdadm --create --verbose /dev/md2 -l 1 -x 0 -n 2 /dev/sdb3 /dev/sdc3
If you do not have the second mirror at hand, you can put missing instead of any device. The md device will be created in degraded mode and you can attach the other disk later:
# mdadm --create --verbose /dev/md2 -l 1 -x 0 -n 2 /dev/sdb3 missing
How to stop (remove) a md raid device:
# mdadm --manage --stop /dev/md4 mdadm: stopped /dev/md4
How to start (assemble) a previously created raid device:
# mdadm --assemble /dev/md0 mdadm: /dev/md0 not identified in config file. # mdadm --examine --scan ARRAY /dev/md/0 metadata=1.2 UUID=9c97d:435:cc1:d0643 name=pluto:0 # echo "ARRAY /dev/md/0 metadata=1.2 UUID=9c97d:435:cc1:d0643 name=pluto:0" >> /etc/mdadm/mdadm.conf # mdadm --assemble /dev/md0 mdadm: /dev/md0 has been started with 2 drives.
How to revert mdadm auto-read-only:
core:vbox# cat /proc/mdstat Personalities : [raid1] md0 : active (auto-read-only) raid1 sda1[0] sdb1[1] 256896 blocks [2/2] [UU] unused devices: <none> core:vbox# mdadm --readwrite /dev/md0 core:vbox# cat /proc/mdstat Personalities : [raid1] md0 : active raid1 sda1[0] sdb1[1] 256896 blocks [2/2] [UU] unused devices: <none>
The option --readwrite from the example above works also when you have resync=PENDING.
root@pluto:~# cat /proc/mdstat Personalities : [raid1] md0 : active (auto-read-only) raid1 dm-8[1] dm-7[0] 209584000 blocks super 1.2 [2/2] [UU] resync=PENDING unused devices: <none>
How to resize a md device:
mdadm --grow --size=max /dev/md2
How to get details about a md device:
core:linux# mdadm --query --detail /dev/md0 /dev/md0: Version : 0.90 Creation Time : Fri Nov 13 20:12:39 2009 Raid Level : raid1 Array Size : 256896 (250.92 MiB 263.06 MB) Used Dev Size : 256896 (250.92 MiB 263.06 MB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 0 Persistence : Superblock is persistent Update Time : Sat Dec 13 01:28:07 2014 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 UUID : 9c97d:435:cc1:d0643 Events : 0.5174 Number Major Minor RaidDevice State 0 8 1 0 active sync /dev/sda1 1 8 17 1 active sync /dev/sdb1