A Note Extending the Analysis of Two-Head Disk Systems to More General Seek-Time Characteristics

We analyze a model of a movable-head disk system with two read/write heads maintained a fixed distance d apart on each arm. Successive request-addresses are assumed to be independent random variables, uniformly distributed over the set of cylinders. The purpose of an earlier analysis was to find that value of d which minimizes the expected seek time per request, assuming that seek time varies linearly with the distance z traveled by the heads. In this note, we extend this analysis to more general seek-time characteristics which take into account nonlinear acceleration effects. Detailed results, combining both analysis and simulation experiments, are presented for seek times linear in zα 0  α  1. An unexpected result of the study was that the value of d which minimizes expected seek time is very nearly independent of α. © 1989 IEEE

Duke Scholars

Author Robert Calderbank Computer Science