Evaluation of Fault-Tolerant Software: A Performability Modeling Approach

A comparative evaluation of recovery blocks and N-version programming (N = 3) is accomplished by means of performability modeling. For each scheme, a corresponding stochastic process model is constructed by employing a hierarchical modeling framework. Comparison is based on a performability measure that quantifies software “effectiveness” in a designated operational environment. The evaluation results reveal some interesting differences between the two schemes; in addition, they point to certain inadequacies in the use of computational redundancy which could serve as the basis for design modification.