Fuzzy reliability of gracefully degradable computing systems

Conventional reliability analysis rely on the probability model, which is often inappropriate for handling complex systems due to the lack of sufficient probabilistic information. For large complex systems made up of many components, the uncertainty of each individual parameter amplifies the uncertainty of the total system reliability. To overcome this problem, the concept of fuzzy approach has been used in the evaluation of the reliability of a system. In this paper, we use a gracefully degradable redundant computing system to capture the effect of coverage factor and repair on its reliability. Markov models on the other hand can handle degradation, imperfect fault coverage, complex repair policies, multi-operational-state components, dependent failures, and other sequence dependent events. In order to have the advantages of both fuzzy and Markov approaches, an attempt has been made to develop a fuzzy based Markov model.