Rebuild options in RAID5 disk arrays

Abstract

The response time of disk accesses in RAID5 disk arrays degrades when one of the N + 1 disks fails and there is a further degradation by the interference caused by rebuild processing. In addition to giving user accesses a higher non-preemptive priority over track reads for rebuild, we consider: (i) the read redirection option; (ii) split-seek option, i.e., allowing user requests to preempt track reads after a seek is completed; (iii) the split-latency/transfer option, i.e., allowing user requests to preempt track reads, Simulation results show that for lower disk utilizations the split-latency/transfer option is desirable in that it reduces response time, while not increasing rebuild time considerably. At higher disk utilizations the response time attained by the split-latency transfer option is comparable to that attained by less preemptive options with shorter rebuild times. A new metric, excess cumulative response time, is defined to compare the efficiency of rebuild options.