RAID 10?

  • i've lost a raid 10 array so proof that backups are still a must.
    how did i lose it? the raid card got zapped and along with it the 4 drives that were connected to it.
    now as a bit of a wrestle with it and not giving up on recovery, i'm thinking of getting some circuit boards for the drives as i'm convinced it's not mechanical.
    so, as it's a RAID 10, you can lose 2 drives out of the array as opposed to 1 from a RAID 5.
    but which 2 do you need to recover? 1+2, 3+4, 1+3, 2+4?

  • As you have discovered, RAID protects against failure of the drives. A RAID controller failure brings down the whole thing! To avoid that you need dual-channel disks that can connect to multiple controllers and software that knows how to handle the multiple paths to disks… Then if the multiple RAID controllers are on the same system bus, failure of that bus brings it all down... You need multiple hosts, each with fibre-channel (or whatever) controllers to dual-ported disks, and clustering ability...
    The numbering of disk allocation in RAID will depend on the particular firmware implementation. e.g. a 4 disk RAID10 set might have disk 1+3 mirrored (set A) and 2+4 mirrored (set B). Then the logical blocks are striped across set A and set B. In that case you can lose 1 disk from set A  and 1 disk from set B and users don't notice. But if you lose 2 disks from set A, or 2 disks from set B, you are dead. So, you can't lose just any 2 drives.
    The other hassle with RAID is that the firmware usually writes some custom stuff at the start of the disks, and the ordinary boot block is not where it would be on an ordinary disk. So, even if you are just doing RAID1 (mirrored pair), and the RAID controller has died, you can't just plug 1 of the disks into an ordinary disk controller and have it boot - this can be VERY annoying when trying to get something up and running temporarily.

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