There are two key issues in the process of obtaining input parameters for performance models: parameter measurement and parameter estimation. With regard to measurement, it is essential to understand what is being measured, how accurate the measurements are, and how reliable the resulting numbers are. In this chapter several aspects of the measurement process were discussed. In addition, several techniques used for monitoring the level of activity of a computer system were highlighted.
Parameter estimation deals with the determination of input parameters from secondary measurement data sources. Many times, monitors do not provide enough information for calculating the input parameters required by a performance model. Assumptions have to be made regarding the behavior of the system and inferences are made in order to derive the desired parameters.
Although this chapter does not focus on any particular product or manufacturer, it provides a set of general guidelines for transforming typical measurement data into the required input parameters for performance models. The guidelines can be applied to real problems in a straightforward manner. Because of the uncertainties associated with the process of estimating parameters, model validation is an indispensable step in the overall modeling process.