Reliability optimization of redundant software with correlated failures

Several authors have addressed the problem of reliability optimization of modular software with redundancy. At present, these approaches seem to be limited by the fact that they use statistical independence assumptions for different program versions. In view of strong empirical evidence of positive failure correlations between program versions, it is desirable to generalize these reliability optimization techniques by taking such correlations explicitly into consideration. In the presented paper, this is done based on a multiversion software failure correlation model tracing back to D.E Eckhardt and L.D. Lee (1985). We show how taking failure correlation into account extends the corresponding optimization problems, and how they can be treated computationally. In particular, in the (practically relevant) case of components with relatively high reliability, the optimization problems reduce to knapsack type problems which can, for relevant problem sizes, be solved with rather low computational effort. Also for the general case, solution techniques are outlined.