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I've been tasked with restoring a RAID from a failed Buffalo NAS. the NAS box has failed, but our understanding at this point is that the drives are still functioning. I believe that Buffalo's NAS was using mdraid+Linux in a RAID5 of 4x1TB drives. my understanding of mdadm is that it's not smart enough to figure out the correct striping of the drives by itself.

I've seen a DEFCON presentation on "Rebuilding RAID By Sight and Sound", so I know some techniques for manually determining the order if I can get access to the drives. I'm not sure how to go about working on these in a non-destructive way. I'm not sure I can even get access to 4TB of scratch space for storing working images.

I'll update as I go/research, but some pointers on how to proceed would be appreciated!

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up vote 1 down vote accepted

I'm pretty sure that mdadm will Just Work. It can already tell the position of a drive in an array, for example:

# mdadm -Q /dev/sda
/dev/sda: is not an md array
/dev/sda: device 3 in a 3 device unknown raid5 array.  Use mdadm --examine for more detail.

And in playing around with a RAID5 array on top of some loop devices, it appears to assemble the array regardless of the order in which the drives are specified:

# mdadm -A /dev/md0 /dev/loop[012]
mdadm: /dev/md0 has been started with 3 drives.

# mdadm -A /dev/md0 /dev/loop[210]
mdadm: /dev/md0 has been started with 3 drives.

I think you're in good shape, assuming the drives are operational and the data is intact. If you can image the drives before working with them then obviously that's the safest thing to do. Maybe you have some friends who are planning drive purchases anyway? You could use the drives briefly for backup purposes and then send them on their way.

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