A while back, my workplace had a medium-sized disc array. That is, something like a hundred UW-SCSI 72GB drives, arranged into about twelve different RAID-5 set

A while back, my workplace had a medium-sized disc array. That is, something like a hundred UW-SCSI 72GB drives, arranged into about twelve different RAID-5 sets. When we had to power it down because of scheduled electrical work in the building, about eight of the drives failed to come up again. It's a miracle none of the RAID-5 sets were broken. Hard drives don't like being switched off if they have been going for a couple of years. And that is why RAID is no substitute for backups, people. A reasonable proportion of events that will take out a hard drive will take out more than one.