Data Recovery Digest

If you are going to have a hard disk fail in a RAID configuration, you want it to be in a RAID 1 configuration. This is even more true if you have multiple disks fail. RAID 1 is one of the most fault tolerant RAID levels, because it consists of mirrored independent disks. This means that if one disk fails, then you can safely bet that the data is still intact on one or more of the other member disks. This is in contrast to RAID 1, RAID 5, RAID 6 and other RAID configurations that use data striping to write blocks of data across several disks.
Data Recovery in RAID 1 After One Failed Disk
A RAID 1 volume has a fault tolerance of N-1 drives. That is, if a RAID 1 has two drives, it can continue functioning if one disk is failed. If a RAID 1 has five drives in it, it can continue functioning if four drives fail. When this happens, data recovery isn’t even necessary. Your RAID 1 volume will continue functioning, albeit in a critical state. You can restore your RAID 1 to a healthy state by replacing the failed disk drive. The data will be rebuilt onto the new disk drive by the RAID controller. If you are concerned that the other disks on a RAID 1 may also fail, you can take it offline and back up the data.
Data Recovery in RAID 1 After Multiple Failed Disks
If all the disks in a RAID 1 fail or become corrupted, then your RAID will go offline. Although it may appear that all of your drives have failed, the actual cause may be the RAID controller or a corrupted header data on the drive or volume. If this is the case, you should be able to remove each disk from the RAID controller and attempt to mount it as an independent disk (make sure you choose the right file system). However, if there is a chance that the disk is physically faulty (but not completely failed yet), you should proceed with caution. Do not attempt to force the disk to mount, either in a RAID configuration or otherwise. Instead, attempt to image the disk and then run data recovery operations on the disk image. Repeat this for each member disk. Chances are, different areas on each disk will be damaged. If you are lucky, you will be able to piece together the parts that you’ve recovered from each disk. In the best case scenario, you will be able to repair the disk images to the point where they can be mounted and accessed via the normal file system.
Preventive Maintenance
One last tip: if one drive in a RAID 1 has failed, it’s not infeasible that the other disks may also be nearing the end of their lifespans. Because the drives are mirrored, they’ll likely be experiencing the same ear and tear (not to mention the same environmental conditions). It might be a good idea to replace both the drives. Replace the failed drive first, allow it to rebuild, and then replace the other drive.