102 A Step - by - Step Approach to Capacity Planning

Planning the capacity of a CCS system requires that a series of steps be followed in a systematic way. This chapter starts by providing a clear deenition of what adequate capacity means. It then presents a methodology that leads the capacity planner, in a step-by-step fashion, through the process of determining the most cost-eeective system connguration and networking topology. Investment and personnel plans follow as a consequence. The main steps of the methodology are: understanding the environment, workload characterization, workload model validation and calibration , performance model development, performance model validation and calibration , workload forecasting, performance prediction, cost model development, cost prediction, and costtperformance analysis. The methodology presented here requires the use of three models: a w orkload model, a performance model, and a cost model. The workload model captures the resource demands and workload intensity c haracteristics of the load brought t o t h e system by the diierent t ypes of transactions and requests. The performance model is used to predict response times, utilizations, and throughputs, as a function of the system description and workload parameters. The cost model accounts for software, hardware, telecommunications, and support expenditures. This chapter draws in part on material presented in 77 and Chap. 2 of 88. Various steps of the methodology are discussed in further detail in subsequent c hapters.