A comparison of RAID storage schemes: Reliability and efficiency

In this paper, we compare the reliability and efficiency of RAID (Redundant Array of Independent Disks) schemes for disk-array storage systems. RAID 0 uses no parity at all. RAID 1 through 5 use single parity and striping. RAID 6 uses double parity. Parity involves the addition of redundant bits which are used to detect and correct errors in the original data. Striping involves the spreading of related data in chunks onto different physical disks controlled by different disk controllers in order to minimize the probability of multiple failures. Striping has the additional benefit of improving the system performance by increasing bit transfer rate. An evaluation of the various RAID schemes involves a computation of the number of additional disks needed to achieve improved reliability. The metric used to evaluate efficiency is the ratio of the width of the high reliability region to the total number of physical disks required.