It's been said before, but it bears saying again. Having RAID is not the same thing as having backups, and having backups is not the same thing as having RAID.

RAID is a level of protection against hardware failure, and also is a tool in maintaining uptime. With a hot swap system that supports it, with RAID 1, 5, etc, you can usually suffer a drive failure and replace the drive without having to take your server off-line. If you lose two drives, though, you lose everything. There are RAID levels that can handle more drive failures, but see my other posts for that info.

Something to keep in mind with RAID, though, is that if something happens to corrupt your data, that will just be propagated across the array, and RAID won't save you. Boss's spawn comes in, plays around, deletes all your employee history, RAID won't help you. That's what backups are for.

RAID is pretty awesome and a great tool in your toolbox, but don't let it give you a false sense of security.