The emphasis of my post today is on a RAID 5, 4 disk striped disk array. This drive came out of a Compaq Eserve machine running a hardware driven SCSI controller. The RAID configuration reported no errors when the disks were failing.

17082007230.JPG

We found that two of the hard drives were failing mechanically. These disks needed repair. Once these drives were back up and running, we could start the recovery process. RAID 5 is a very complex data recovery situation where the RAID has to be de striped and then rebuilt.

RAID 3, 4 and 5 use standard parity blocks by using the logical function. For example, given the following three bytes:

• A1 = 00000111
• A2 = 00000101
• A3 = 00000000

Taking the XOR of all of these yields:

a1-a1.bmp

graph