Investigating fault tolerant computing systems reliability

Nowadays, computers and networks represent the heart of a great part of modern technologies. Computing systems are widely used in many application areas, and they are desired to achieve various complex and safety-critical missions. As consequence, greater attention is lavished on performance and dependability evaluation of computing systems. This brings to the specification of precise techniques and models, that consider and evaluate aspects before (consciously or unconsciously) approximated or ignored at all. On the other hand, the increasing importance assumed by such systems is translated in terms of tighter and tighter constraints, requirements and/or policies (QoS, fault tolerance, maintenance, redundancy, etc.) according to the systems´ criticism. The evaluation must therefore take into great account such dynamic behaviors, carefully identifying and quantifying dependencies among devices. In this paper we face the problem of individuating and evaluating the most common dynamic behaviors and dependencies affecting fault tolerant computing systems. We propose some models to represent such aspects in terms of reliability/availability, basing on dynamic reliability block diagrams (DRBD), a new formalism derived from RBD we developed. In this way we want to provide the guidelines for adequately evaluating fault tolerant computing system reliability/availability.