Performance analysis of RAID5 disk arrays with a vacationing server model for rebuild mode operation

Abstract

We analyze the performance of RAID5 disk arrays in normal, degraded, and rebuild modes. The analysis, which is shown to be highly accurate through validation against simulation results, achieves its accuracy by (1) modeling detailed disk characteristics; (2) developing a simple approximation to compute the mean response time for fork-join requests arising in degraded mode operation; and (3) using a vacationing server model with multiple vacation types for rebuild mode analysis. According to this model vacations (rebuild reads) are started when the server (disk) becomes idle and are repeated until the arrival of an external disk request. Type one (two) vacations correspond to the reading of the first track which requires a seek (successive tracks requiring no seeks). The analytic solution is used to quantify the effect of different rebuild options, such as read redirection and the split-seek option.