Striping in Disk Array RM2 Enabling the Tolerance of Double Disk Failures

There is a growing demand in high reliability beyond what current RAID can provide and there are various levels of user demand for data reliability. An efficient data placement scheme called RM2 has been proposed in [Efficient Placement of Parity and Data To Tolerate Two Disk Failures In Disk Array Systems], which makes a disk array system tolerable against double disk failures. In this paper, we consider how to choose an optimal striping unit for RM2 particularly when no workload information is available except read/write ratio. A disk array simulator for RM2 has been developed for experimental works. It is shown that RM2 has an optimal striping unit of two and half tracks in the case of disk read operations, and one third of a single track if any disk write operations are involved.