A General Model for the Performance of Disk Systems

Abstract

The performance of a disk system is often measured in terms of the length of the waiting line or queue of requests for each of the system's spindles. Thus it is natural to formulate and analyze queueing models of disk systems. While most disk systems have certain characteristics, such as channel interference and concurrent seeks, in common, previous analyses have always been begun from scratch, without exploiting this commonality. We introduce a general queueing model for disk systems, which incorporates the characteristics common to most disk systems, and use it in the approximate analyses of models of the IBM 2314 and 3330 disk systems. Comparisons with simulation statistics show that the approximations made are very good over a wide range of arrival rates and system parameters. We also show how to use the analytic results to investigate performance differences between devices.