Comparing Software Rejuvenation Policies under Different Dependability Measures

Tadashi DOHI  Hiroaki SUZUKI  Kishor S. TRIVEDI  

IEICE TRANSACTIONS on Information and Systems   Vol.E87-D   No.8   pp.2078-2085
Publication Date: 2004/08/01
Online ISSN: 
Print ISSN: 0916-8532
Type of Manuscript: PAPER
Category: Dependable Computing
software rejuvenation,  software aging,  system availability,  mean up rate,  preventive maintenance,  numerical optimization,  fault management,  design diversity,  

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Software rejuvenation is a preventive and proactive solution that is particularly useful for counteracting the phenomenon of software aging. In this paper, we consider both the periodic and non-periodic software rejuvenation policies under different dependability measures. As is well known, the steady-state system availability is the probability that the software system is operating in the steady state and, at the same time, is often regarded as the mean up rate in the system operation period. We show that the mean up rate should be defined as the mean value of up rate, but not as the mean up time per mean operation time. We derive numerically the optimal software rejuvenation policies which maximize the steady-state system availability and the mean up rate, respectively, for each periodic or non-periodic model. Numerical examples show that the real mean up rate is always smaller than the system availability in the steady state and that the availability overestimates the ratio of operative time of the software system.