Object Storage in Cloud Computing Environments: An Availability Analysis

Object Storage Systems (OSSs) have been conceived to manage a bulk of highly unstructured data (videos, images, social resources etc.) by storing them in the form of objects accessible via REST APIs. An interesting implementation of OSS is based on Swift, a component of OpenStack, the most important platform exploited to deploy the Infrastructure as a Service (IaaS) paradigm. The present work is aimed at characterizing a Swift-based OSS from the availability point of view, namely at finding out the best configuration able to guarantee the socalled “five nines” availability requirement allowing a maximum system downtime of a little more than five minutes per year. The availability analysis is faced by exploiting the Stochastic Reward Nets (SRNs) formalism, accounting for the probabilistic behavior of the underlying structure of the Object Storage System. More specifically, the OSS availability has been assessed by performing a steady-state analysis whereas a sensitivity analysis has been carried out to evaluate the robustness of the overall system with respect to variations of some key parameters.