Highly reliable two-dimensional RAID arrays for archival storage

We present a two-dimensional RAID architecture that is specifically tailored to the needs of archival storage systems. Our proposal starts with a fairly conventional two-dimensional RAID architecture where each disk belongs to exactly one horizontal and one vertical RAID level 4 stripe. Once the array has been populated, we add a superparity device that contains the exclusive OR of all the contents of all horizontal-or vertical-parity disks. The new organization tolerates all triple disk failures and nearly all quadruple and quintuple disk failures. As a result, it provides mean times to data loss (MTTDLs) more than a hundred times better than those of sets of RAID level 6 stripes with equal capacity and similar parity overhead.