Performability analysis for degradable computer systems

Degradable performance of fault-tolerant computer systems has given rise to considerable interest in mathematical models for combined evaluation of performance and reliability. Most of these models are based upon Markov processes. Several methods have been proposed for the computation of the probability distribution of performability upon an interval of time [0, t]. In this paper, we present a new algorithm based on the uniformization technique to compute this distribution for block degradable models. The main advantage of this method is its low polynomial computational complexity and its numerical stability, since it only deals with a nonincreasing sequence of positive numbers bounded by 1. This important property allows us to determine new truncation steps which improve the execution time of the algorithm. We apply this method to a degradable computer system.