Stochastic activity networks (SANs) are a stochastic generalization of Petri nets. The original definition of SANs has been used as a modeling formalism in several well-known and powerful modeling tools. SANs have been used to evaluate a wide range of systems, mainly for dependability and performability evaluation purposes. SAN models have not been considered in the definition of the Petri net ...

The widespread integration of virtualization technologies in data centers has enabled in the last few years several benefits in terms of operating costs and flexibility. These benefits maybe boosted through join optimization of power management (PM) and dependability for virtualized systems. This indeed involves developing appropriate models to better understand their performability behavior wh...

Over the last decade considerable effort has been put in the development of techniques to assess the performance and the dependability of computer and communication systems in an integrated way. This so-called per-formability modelling becomes especially useful when the system under study can operate partially, which is for instance the case for fault-tolerant computer systems and distributed s...

This paper develops time-based rejuvenation policies to improve the performability measures of a cluster system. Three rejuvenation policies, namely standard rejuvenation, delayed rejuvenation and mixed rejuvenation, are designed to improve the cluster’s performability under varying workload. Analytic models are built to evaluate these three policies. Since deterministic transitions are used in...

ed framework for the performability evaluation of fault-tolerant computer systems," IEEE Transac

The performability of a system is usually evaluated as the mean of a performance measure, aggregated over all failure scenarios (both tolerated and not) through a Markov reward process. This metric can gloss over performance deficiencies in important portions of the failure scenario space, and is also expensive to compute because the number of possible failure scenarios can be very large. We ar...

Performability modelling and analysis is used as a measure of both performance and dependability of, mainly, fault-tolerant systems. Proxels are a paradigm that provides deterministic analysis of discrete stochastic models which contain general types of distribution functions, which is not otherwise possible using the standard approaches, such as discrete-event simulation or Markov reward model...

Markov Decision Processes (MDPs) and Partially Observable MDPs (POMDPs) have been proposed as a framework for performability management. However, exact solution of even small POMDPs is very difficult because of their potentially infinite induced state spaces. In this paper, we present new lower bounds on the accumulated reward measure for MDPs and POMDPs. We describe how the bounds can be used ...