Updated at 2012-11-22 16:22
RAID stands for Redundant Array of Inexpensive (Independent) Disks.
RAID 0 = 2 or more disks, excellent performance, no copies. RAID 1 = 2 or more disks, good performance, excellent copies. RAID 5 = 3 or more disks, good performance, good copies, use for read oriented. RAID 10 = 4 or more disks, excellent performance, excellent copies, best.
Consider using RAID 10 for main database, RAID 1 for transaction logs and RAID 1 for the boot disk.