P2P storage systems modeling, analysis and evaluation

This Report characterizes the performance of peer-to-peer storage systems in terms of the delivered data lifetime and data availability. Two schemes for recovering lost data are modeled and analyzed: the first is centralized and relies on a server that recovers multiple losses at once, whereas the second is distributed and recovers one loss at a time. For each scheme, we propose a basic Markovian model where the availability of peers is exponentially distributed, and a more elaborate model where the latter is hyper-exponentially distributed. Our models equally apply to many distributed environments as shown through numerical computations. These allow to assess the impact of each system parameter on the performance. In particular, we provide guidelines on how to tune the system parameters in order to provide desired lifetime and/or availability of data. One important outcome of our analysis is that a simplifying exponential assumption on the peers availability leads to incorrect evaluation of the performance achieved. Thereby, the more elaborate model is necessary to capture the true behavior of peer-to-peer storage systems