SYSTEM AVAILABILITY ESTIMATOR.

Abstract

The system availability estimator (SAVE) program package is described that can be used for constructing and solving probabilistic models of computer system availability and reliability. SAVE is a state-of-the-art tool intended for use during system design and configuration. SAVE has a high-level user-friendly interface and is capable of solving much larger models (tens of thousands of states) than existing availability and reliability modeling packages. The system to be modeled is specified at the block diagram level. Parameters specifying failure rates, repair rates, operational and repair dependencies, common-mode failure occurrences, and use of spare components in hot-standby mode may be defined for each component being modeled. Evaluation criteria are given which specify the conditions under which the system is considered to be operational. A continuous-time Markov chain model is automatically constructed and solved and user-specified measures, namely, steady-state availability, interval availability, reliability and the mean time to failure are computed. In addition, the sensitivities (derivatives) of steady-state availability with respect to user-specified input parameters are computed to aid in improving system availability.