Availability and Reliability Modeling for Computer Systems

Dependability calculates the capability of a product to deliver its intended level of service to the user, especially in light of failures or other incidents that impinge on its performance, and combines various underlying ideas, such as reliability, maintainability, availability, and user demand patterns, into a basic overall measure of quality, which customers use along with cost and performance to evaluate products. This chapter describes the computer system dependability analysis and its types, different classes of dependability measures, Markov and Markov reward models commonly involved for dependability analysis and their solution methods. The three classes of dependability measures are system availability measures, system reliability measures, and task completion measures. The chapter also describes four types of dependability analyses: evaluation, sensitivity analysis, specification determination, and tradeoff analysis. A model-based evaluation, or sometimes a hybrid approach based on a judicious combination of models and measurements, is used for cost-effective dependability analysis. The chapter discusses the determination of the parameters, such as failure rates, coverage probabilities, repair rates, and reward rates as well as model verification and validation. The chapter also demonstrates the use of these methods, a detailed dependability analysis on a full-system example representative of existing computer systems. © 1990 Academic Press Inc.