Today I found myself with a degraded RAID array after a power outage last night. (Yes I know UPS would be useful..) One drive had failed and I have a RAID 5 with three drives and one drive failed. Additionally, since there was some extra room, for some reason I had another RAID 1 array across two of the drives..not sure what I was thinking when I set that up. I found the following guide quite helpful:
I also made use of the cfdisk tool since I had to create the partitions manually before adding the partitions to the arrays.
Update: Got a UPS for my birthday, so hopefully the weird power troubles my house has been having won't be able to kill anymore hard drives :D