Tag: Hardware
RAID 5 and Write Holes
by CharlesJP on Oct.28, 2009, under Uncategorized
I believe I have experienced the RAID 5 Write Hole.. I had a server that crashed on Friday and when I got to it, it was at the BIOS screen ready to enter the RAID controller. I saw that a drive was amber, so I popped in a spare and began a rebuild. When it came back up, the server blue-screened immediately and restarted itself. After that, Active Directory wouldn’t start because of a corrupt database. What it appears happened, is that the parity information was corrupted because of the write hole. Whether this happened at the time the drive failed or at a previous time I’m not sure.
Write Holes:
I had never previously experienced this before, so a write hole was a new concept for me. The flaw behind RAID5 is that since the raid controller cannot write to all disks at once in the RAID, plus calculate the parity information to write, there are seconds that if something interrupts the write process, the parity information can become incorrect. Then when you try to do a rebuild process, the parity is incorrect, and thus the drive will be rebuilt with the wrong data, and then things are corrupt.
