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I have a Linux RAID6 array (mdadm) composed of 8 disks.

2 disks failed. I replaced them, now I have 2 new empty disks. I would like to rebuild the raid

but when I start a raid rebuild, the rebuild fails because a third disk is showing read errors and get ejected of the array.

It's ok to loose data on the few sectors producing read errors.

(What is | is there any) way to recover the raid array ?

  • an idea is to ddrescue the 3rd failing disk on one of the new disk already inserted. – exeral Aug 31 '15 at 13:36
  • Do you still have the first 2 disks which failed? Can any data be recovered from those? – kasperd Aug 31 '15 at 16:04
  • no, these disks does not even power on – exeral Sep 1 '15 at 13:41
  • There are companies which specialize in data recovery. You could send the disks which you cannot power on to two different such companies. As long as one of them succeed, you should be able to recover all of the data. How to reassemble all the pieces of data afterwards is unfortunately something, which I don't know. – kasperd Sep 1 '15 at 13:55
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You may be able to use a tool like ddrescue to image that 3rd failed drive to one of the new drives. This should be an exact copy minus the bad blocks. This way it won't get read errors. Then replace that 3rd failed drive with the newly imaged one.

Assuming none of the bad blocks were critical to the RAID or filesystem then you may be able to then assemble the array in degraded mode and either copy as much data off as possible, or try adding more drives for the rebuild/resync (the latter being more risky IMO).

  • yea that was my idea too. but, the mdadm superblock is replicated. the new drive is /dev/sdd but the superblock still talks about /dev/sdh (the buggy drive) do I need to "edit" superblock or can add it as is – exeral Sep 1 '15 at 13:42
  • after replicating the drive you need to physically remove the old bad drive because it will have the same UUID. Of course you could wipe the superblock on the old bad drive but that would be a really bad idea. – CR. Sep 1 '15 at 13:45

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