A model of the UNIX time-sharing system under disk saturation

A deterministic model of the UNIX time-sharing system under disk saturation is presented and a performance experiment on a PDP-11/34 is conducted to establish the validity and accuracy of the model. The basis of the model is that the ratio of mean file system access rates between two different systems can provide, under certain circumstances, a useful performance comparison between the two systems. Given several workload and system parameters as well as the elapsed time to perform the workload, the model predicts from a second set of parameters the elapsed time to perform the second workload. Workload, hardware, and internal system parameters are identified and tools are constructed to record these parameters. A controlled experiment, using a synthetic workload, is then conducted. The results are analyzed and the model is evaluated. The model is extended in response to regularities discovered in the measurement data. Sample applications of the model are given. The suitability of the tools developed and the methods used are discussed.Science, Faculty ofComputer Science, Department ofGraduat