I have a server with a RAID LSI Logic / Symbios Logic MegaRAID SAS 2108 [Liberator] and 4 disks of 3TB attached, configured as RAID 5. Unfortunately after 3 years of good services one disk died (the plates are gone) and another one have some bad sectors.

I need to recovery some data from 2 days ago but I can't mount and/or find a way to do that. How I don't know the right way to recovery some data, I stop the server and I'm asking for help.

What steps can I take to recover the data on the array?

  • Can you clarify this question a bit? Please add at least a RAID level and what was a file system. – kworr Dec 15 '15 at 21:04
  • Yes, sure. 4 disks of 3TB each in one volume in RAID 5. One of the disks is dead and I can't recovery the data or use the volume. – pmichelazzo Dec 16 '15 at 2:32

This is a "classical" problem on RAID5 arrays: when one disk die, you discover the others have developped bad sectors. Under this circumstance, many hardware RAID controllers simply drop the entire array (or refuse to start it).

If your RAID controller has a "forced" mode to bring the array online (albeit with some unavoidable data corruption), use it.

If not, you should be able to recover doing that:

  1. obtain a disk identical to the one with bad sectors
  2. connect the two disks to a Linux box with ddrescue (or dd_rescue, in Debian parlance)
  3. copy the old disk to the new one using the command ddrescue <bad_drive> <new_drive>
  4. let it finish and then connect the new drive to your RAID controller, in the same slot/position assigned to the bad one
  5. your array should go online, albeit with some unavoidable data corruption.
  6. do a complete filesystem check on the vdisk/array

If you are lucky, the corrupted data reside in the free/unallocated space, resulting in no data loss.

Otherwise, you risk losing something. If this is an unacceptable risk, forgot the step above: destroy/recreate your array and restore from backups.

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