Self-similarity in I/O workload: analysis and modeling

Abstract

Recently, the notion of self-similarity has been applied to wide-area and local-area network traffic. This paper demonstrates that disk-level I/O requests are self-similar in nature. We show evidence, both visual and mathematical, that the I/O accesses are consistent with self-similarity. Moreover, we show that this property of I/O accesses is mainly due to writes. For our experiments, we use two sets of traces that collect the disk activity from two systems over a period of two months. Such behavior has serious implications for the performance evaluation of storage subsystem designs and implementations, since commonly-used simplifying assumptions about workload characteristics (e.g. Poisson arrivals) are shown to be incorrect. Using the ON/OFF model, we implement a disk request generator. The inputs of this generator are the measured properties of the available trace data. We analyze the synthesized workload and confirm that it exhibits the correct self-similar behavior.