Maximizing performance in a striped disk array

Abstract

Improvements in disk speeds have not kept up with improvements in processor and memory speeds. One way to correct the resulting speed mismatch is to stripe data across many disks. The authors address how to stripe data to get maximum performance from the disks. Specifically, they examine how to choose the striping unit, that is, the amount of logically contiguous data on each disk. Rules for determining the best striping unit for a given range of workloads are synthesized. It is shown how the choice of striping unit depends on only two parameters: (1) the number of outstanding requests in the disk system at any given time, and (2) the average positioning time × data transfer rate of the disks. The authors derive an equation for the optimal striping unit as a function of these two parameters; they also show how to choose the striping unit without prior knowledge about the workload.