Numerical analysis of gracefully degrading fault-tolerant computer systems: Semi-Markov and Laguerre transform approach

A gracefully degrading fault-tolerant computer system is considered where the system performance deteriorates through several stages depending on its configuration. The usual exponentiality assumption is totally eliminated and the model is based on a semi-Markov approach. By exploring the underlying linear structure of the model, efficient numerical procedures are developed for computation of variety of performability measures via the Laguerre transform. A tradeoff regarding when to repair the whole system is also discussed. A numerical example captures the almost periodic nature of the system, thereby demonstrating the importance of the dynamic analysis. Also, the impact of the common exponentiality assumption on performance measures is investigated through the example.