Segregated failures model for availability evaluation of fault-tolerant systems

This paper presents a method of estimating the availability of fault-tolerant computer systems with several recovery procedures. A segregated failures model has been proposed recently for this purpose. This paper provides further analysis and extension of this model. The segregated failures model is compared with a Markov chain model and is extended for the situation when the coverage factor is unknown and failure escalation rates must be used instead. This situation is illustrated in detail by estimating availability of a Lucent Technologies Reliable Clustered Computing architecture. For this example, numeric values are provided for availability indexes and the contribution of each recovery procedure to total system availability is analysed.