Think of RAID as a mechanism for taking a number of disk drives and combining them in sort of an array, if you like, such that the availability of data is actually improved or the performance of the total RAID system is improved. So, really there are two dimensions that you look for from RAID - the performance dimension and the availability dimension. A RAID is a method of ganging up, so to speak, a bunch of disk drives, such that the availability and/or the performance is actually improved. Read this transcript for more basics of RAID.