Increased Reliability with SSPiRAL Data Layouts

We evaluate the reliability of storage system schemes consisting of an equal numbers of data disks and parity disks where each parity disk contains the exclusive or (XOR) of two or three of the data disks. These schemes are instances of Survivable Storage using Parity in Redundant Array Layouts (SSPiRAL). They have the same storage costs as mirrored organizations and use very simple parity schemes. Through a novel dynamic analysis of the likelihood of data losses, we show that these schemes are one hundred thousand to a million times less likely to lose data than a comparable mirrored organization. We also found that schemes where each parity disk contains the exclusive or of three data disks performed much better than schemes where each parity disk contains the exclusive or of only two data disks.