Abstract

A bstract — This paper explores how choice of sparing methods impacts the performance of RAID level 5 (or parity striped) disk arrays. The three sparing methods exam”ned are dedicated sparing, distributed sparing, and parity sparing. For database type workloads with random single block reads and writes, array performance is compared in four dl~erent modes- normal mode (no disks have failed), degraded mode (a disk has failed and its data has not been reconstructed), rebuild mode (a disk has failed and its data is being reconstructed), and copyback mode (which is needed for distributed sparing and parity sparing when failed disks are replaced with new disks). Attention is concentrated on small disk subsystems (fewer than 32 disks) where choice of sparing method has signl~cant impact on array performance, rather than large disk subsystems (64 or more disks). It is concluded that, for disk subsystems with a small number of disks, o%tributed sparing oflers major advantages ovev dedicated sparing in normal, degraded and rebuild modes of operation, even cf one has to pay a copyback penalty. Furthermore, it is better than parity sparing in rebuild mode and similar to it in other operating modes, making it the sparing method of choice. 1.

Citations