80 Int. J. Strategic Engineering Asset Management, Vol. 2, No. 1, 2014 Availability and performability analysis for a service degradation process with condition-based preventive maintenance I – formulation and optimisation Tadashi Dohi Department of Information Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527, Japan E-mail: dohi@rel.hiroshima-u.ac.jp Abstract: The preventive maintenance is very useful to improve effectively the service availability for software systems with service degradation. In this paper, we present a stochastic model to describe an operational software system, which consists of one operating system and multiple applications and provides a service in continuous time. Two kinds of rejuvenation strategies are taken, namely reconfiguration of applications as a corrective maintenance and reinstallation of an operating system as a preventive maintenance. We derive the optimal preventive rejuvenation schedules maximising the steady-state service availability and maximising the expected reward per unit time, by means of semi-Markov decision processes. Illustrative numerical examples are presented to give decision tables on the optimal software rejuvenation policies. Keywords: software service; service degradation; software rejuvenation; condition-based maintenance; semi-Markov decision process; optimality; control-limit policy. Reference to this paper should be made as follows: Dohi, T. (2014) ‘Availability and performability analysis for a service degradation process with condition-based preventive maintenance I – formulation and optimisation’, Int. J. Strategic Engineering Asset Management, Vol. 2, No. 1, pp.80–97. Biographical notes: Tadashi Dohi received his BSc (Engineering), MSc (Engineering) and PhD (Engineering) from Hiroshima University, Japan, in 1989, 1991 and 1995, respectively. In 1992, he joined the Department of Industrial and Systems Engineering, Hiroshima University, Japan as an Assistant Professor. Since 2002, he has been working as a Full Professor in the Department of Information Engineering, Graduate School of Engineering, Hiroshima University. In 1992 and 2000, he was a Visiting Research Scholar in University of British Columbia, Canada and Duke University, USA, respectively, on leave of absence from Hiroshima University. His research areas include software reliability engineering, dependable computing and performance evaluation. He is a regular member of ORSJ, REAJ, IEICE, IPSJ and IEEE. Copyright © 2014 Inderscience Enterprises Ltd.