Using Shared Parity Disks to Improve the Reliability of RAID Arrays

This paper proposes to increase the reliability of RAID level 5 arrays used for storing archival data. First, the authors identify groups of two or three identical RAID arrays. Second, the authors add to each group a shared parity disk containing the diagonal parities of their arrays. This paper shows that the new organization can tolerate all double disk failures and between 75 and 89 percent of triple disk failures without incurring any data loss. As a result, the additional parity disk increases the mean time to data loss of the arrays in the group it protects by at least 14,000 percent.