The Design and Evaluation of RAID 5 and Parity Striping Disk Array Architectures

Abstract

In this paper, we evaluate the performance of two disk array architectures, RAID 5 and parity striping, for small I/O applications such as transaction processing systems and workstation environments. We propose solutions to the write synchronization problem which give priority to parity block updates and develop a priority queueing model for describing the behavior of one of these solutions in both architectures. The performance of these two architectures is examined using this model under a wide variety of workloads, where each request may access multiple data blocks. Arbitrary distributions for the request size and skewed access patterns are considered. The results show that the performance of RAID 5 is sensitive to the mean request size but not to the skew in the access pattern when the striping unit is small, whereas the parity striping architecture is sensitive to the skew in the access pattern. Workloads are identified for which RAID 5 and parity striping each provide the best performance. As the behavior of these architectures is necessarily complex, a number of assumptions are made to make the analysis tractable. The effects of these assumptions are minimal and the model predictions are shown to compare well with simulation.