ABSTRACT
Our first goal is to develop load-dependent models of disk units that have a moderate level of complexity suitable for engineering practice. The presented disk unit models describe disk access times, head movement optimization, and disk caching. These models are then used for creating MVA models of disk subsystems. Our second goal is to investigate and exemplify the limits of numerical accuracy of presented queuing models, and to propose indicators of predictive power of analyzed models. We present case studies of disk subsystem modeling of a VAX under VMS and a PC under Windows NT. They provide a good insight into the level of difficulty encountered in practical disk subsystem modeling and help establish realistic expectations of modeling errors. The relative simplicity of MVA models makes them attractive for practice. They can be easily combined with our disk unit models. However, our experiments with MVA models show that only the load-dependent version of MVA generates results with reasonable accuracy.
