All enterprise storage systems depend on disk arrays to satisfy their capacity, reliability, and availability requirements. Performance models of disk arrays are useful in understanding the behavior of these storage systems and predicting their performance. We extend prior disk array modeling work by developing an analytical disk array model that incorporates the effects of workload sequentiality, read-ahead caching, write-back caching, and other complex optimizations incorporated into most disk arrays. The model is computationally simple and scales easily, making it potentially useful to performance engineers.