Processor, I/O path, and DASD configuration capacity

A simple nonlinear procedure is outlined to-size host configurations that can process workload at specified rates. When workload processing involves multiple components of a given kind, doubling the processing rate requires more than doubling the resources. This law of diminishing returns is invariably overlooked even by experienced systems specialists. This paper attempts to shed light on this situation. Workloads are characterized by three parameters: relative I/O content, I/O path, and DASD service time requirements. Workload processing implies a fourth parameter: I/Os processed within unit time. Several workloads have been analyzedto obtain representative estimates of these parameters when specific information is not otherwise available. This characterization is an acceptable first estimate and one that has been found usable for host system capacity planning.