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Can I re-assemble my RAID 5 on only 2 drives using mdadm to recover my data?

Unix & Linux Asked by user203520 on December 8, 2020

I have a 3 drives RAID 5 on a CentOS NAS but 1 drive died. Since then, CentOS boot in emergency mode and I can’t manage to get access to my data.

I tried mdadm --assemble --scan and command returns mdadm: /dev/md2 assembled from 1 drive - not enough to start the array while I have 2 disks running.

Is it possible to rebuild RAID 5 on the 2 remaining disks using mdadm ?

One Answer

It looks like you have an out-of-date RAID superblock. Did one disk fail (removed from the array) and then another one died?

Does mdadm --assemble --force -v ... work?

You should be able to rebuild the superblock with for example mdadm --create /dev/md0 --level=5 --raid-devices=3 --assume-clean /dev/sde1 /dev/sdf1 missing

But you may have inconsistent data in case of a double failure, and possibly another disk failing. If you get the array back, mount read-only and try to recover most important data first.

Check this answer.

Correct answer by John Lee McMahon on December 8, 2020

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