Transmission Capacity of Disk Storage Systems with Concurrent Arm Positioning

Abstract

An organization for a disk storage system oriented toward multicomputer and shared computer applications is described, and a study is made of its effectiveness in accessing data. The disk file incorporates an independently positioned arm for accessing each disk, and the capability for concurrently controlling several positioners. Also, multiple data transmission channels can be provided between the disk file and a buffer unit. A criterion of maximum average transmission capacity is proposed for investigating the speed of accessing data with this organization. Probabilistic models for analyzing the queueing of positioned arms for access to a disk-buffer transmission channel are developed. With reasonable assumptions, the solution of the models is reduced to a small set of linear equations in terms of queue length probabilities. The transmission capacity is evaluated with parameter values typical of contemporary disk files. The principal conclusion is that the economic feasibility of more than three position controllers per disk-buffer channel is very doubtful in seeking the full effectiveness of this organization.