Reliability modeling of the MARS system: a case study in the use of different tools and techniques

Analytical reliability modeling is a promising method for predicting the reliability of different architectural variants and to perform trade-off studies at design time. However, generating a computationally tractable analytic model implies in general an abstraction and idealization of the real system. Construction of such a tractable model is not an exact science, and as such, it depends on the modeler´s intuition and experience. This freedom can be used in formulating the same problem by more than one approach. Such a N-version modeling approach increases the confidence in the results. In this paper, we analyze the MARS architecture with the dependability evaluation tools SHARPE and SPNP, employing several different techniques including: hierarchical modeling, stochastic Petri nets, folding of stochastic Petri nets, and state truncation. The authors critically examine these techniques for their practicability in modeling complex fault-tolerant computer architectures