A method of evaluating mass storage effects on system performance

A significant proportion of the cost and usefulness of a computing system lies in its configuration of direct access mass storage. A frequent problem for computing installation management is evaluating the desirability of a change in the mass storage configuration. This problem often manifests itself in the need for quantitative decision criteria for adding a fast(er) direct access device such as a drum, disk or bulk core to a configuration which already includes direct access disk devices. The decision criteria are hopefully some reasonably accurate cost versus performance functions. This paper discusses a technique for quantifying the system performance gains which could be reasonably expected due to the addition of a proposed fast access device to the system configuration. It should be noted that the measurement and analysis techniques are not restricted to the specific question of an addition to the configuration. That particular question has been chosen in the hope that it will serve as an understandable illustration for the reader and in the knowledge that it has been a useful application for the author.