In this paper, we propose a framework to analyze Markov reward models, which are commonly used in system performability analysis. The framework builds on a set of analytical tools developed for a class of stochastic processes referred to as Stochastic Hybrid Systems (SHS). The state space of an SHS is comprised of: i) a discrete state that describes the possible configurations/modes that a syst...

This paper introduces an analytical method for approximating the performability of a firm realtime system modeled by a multi-server queue. The service discipline in the queue is earliestdeadline-first (EDF), which is an optimal scheduling algorithm. Real-time jobs with exponentially distributed relative deadlines arrive according to a Poisson process. All jobs have deadlines until the end of se...

Markov reward models are an important formalism by which to obtain dependability and performability measures of computer systems and networks. In this context, it is particularly important to determine the probability distribution function of the reward accumulated during a nite interval. The interval may correspond to the mission period in a mission-critical system , the time between scheduled...

Markov models are commonly used to asses the dependability/performability of fault-tolerant systems. Computation of many dependability/performability measures for repairable fault-tolerant systems requires the transient analysis of irreducible Markov models. Examples of such measures are the unavailability at time and the -expected interval unavailability at time . Randomization (also called un...

The ≼Φ stochastic comparison (≼Φ∈ {≼st, ≼wk, ≼wk∗}) of multidimensional Continuous Time Markov Chains (CTMC)s is an efficient but a complex method for the performability evaluation of computer systems. Different techniques can be applied for the stochastic comparison of Markov chains. The coupling is an intuitive method, and may be applied by comparing the evolution of sample paths due to event...

We consider the impact of different communication architectures on the performability (performance + availability) of cluster-based servers. In particular, we use a combination of fault-injection experiments and analytic modeling to evaluate the performability of two popular communication protocols, TCP and VIA, as the intra-cluster communication substrate of a sophisticated Web server. Our ana...

Fault-tolerant systems with repair-upon-failure strategy can become expensive in terms of labour and time. While postponing these repairs, it is essential to keep the whole system capable to deal with user requests. For this purpose, usually, a threshold value is defined which represents the minimum number of servers the system administrator should keep operative. Highly available multiprocesso...

A new framework for the extension of stochastic Petri nets (SPNs) is introduced in this paper. SPNs are extended by elements providing means for a dynamic optimization of performability measures. A new type of transition is deened ooering a feature for speciication of controlled switching, called reconngura-tion, from one marking of a SPN to another marking. Optional reconnguration transitions ...

If computing system performance is degradable then, as recognized in a number of recent studies, system evaluation must deal simultaneously with aspects of both performance and reliability. One approach is the evaluation of a system's "performability" which, relative to a specified performance variable Y, generally requires solution of the probability distribution function of Y. Prior work on p...

Degradable performance of fault-tolerant computer systems has given rise to considerable interest in mathematical models for combined evaluation of performance and reliability. Most of these models are based upon Markov processes. Several methods have been proposed for the computation of the probability distribution of performability upon an interval of time 0; t]. In this paper, we present a n...