An analytical model to evaluate reliability of cloud computing systems in the presence of QoS requirements

Cloud computing is widely referred as the next generation of computing systems. Reliability is a key metric for assessing performance in such systems. Redundancy and diversity are prevalent approaches to enhance reliability in Cloud Computing Systems (CCS). Proper resource allocation is an alternative approach to reliability improvement in such systems. In contrast to redundancy, appropriate resource allocation can improve system reliability without imposing extra cost. On the other hand, contemplating reliability irrespective of Quality of Service (QoS) requirements may be undesirable in most of CCSs. In this paper, we focus on resource allocation approach and introduce an analytical model in order to analyze system reliability besides considering application and resource constraints. Task precedence structure and QoS are taken into account as the application constraints. Memory and storage limitation of each server as well as maximum communication load on each link are considered as the principle resource constraints. In addition, effect of network topology on system reliability is discussed in detail and the model is extended to cover various network topologies.