the benefit of RAID is if you have 2 (or more) identical drives you can set them up to access data faster (RAID 0) or store same data to both to prevent catastrophical crashers (RAID 1) there are many more kinds but those are the most common. usually you can actually get 2 smaller drives cheaper then 1 larger and RAID them together for faster access times (so buy 2 80gb drives instead of 1 160gb drive)
but if 1 disk in a RAID 0 crashes the other is useless. (DOA. gone. no use unless reformatted)
but if 1 disk in a RAID 0 crashes the other is useless. (DOA. gone. no use unless reformatted)