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Recover from a disk failure
Below is “what worked last time”, but there is more comprehensive documentation elsewhere.
Disconnect the existing RAID array:
$ mdadm --stop /dev/md127
Create a new array out of the working disks:
$ mdadm \
--verbose \
--assemble \
--force \
/dev/md0 \
/dev/sdc1 /dev/sdd1
Try mounting it, check everything’s OK:
$ mount /dev/md0 /mnt/md0
Add the new disk:
$ mdadm --manage /dev/md0 --add /dev/sdb1
Watch it rebuild, and hope:
$ cat /proc/mdstat
Misc
Check the status of the array
$ mdadm --detail /dev/md127
Check the status of an individual disk
$ mdadm --examine /dev/sdb
Check the event counts match
$ mdadm --examine /dev/sd{a,b,c} | grep Event
Identify a physical disk
$ hdparm -I /dev/sda | grep Serial