RAID for novices | Computerworld Blogs:

I know most of you already know this stuff better than you know your families, but I tend to collect articles like this, so that I can copy and paste someone else's words into those rushed business cases...

Disks are connected to a RAID array for the purposes of increased performance and/or increased fault tolerance. RAID arrays also give you the added benefit of combining multiple drives into one contiguous space, which makes disk space management easier.

Even if you're not into selective plagiarism in the interests of expediency, this sort of article, and the one it links to can be very handy to keep around to pass to incoming Junior staff.