Abstract: Reliability is one of the basic connotations of dependability, and it is also the key of P2P Storage Systems study. P2P storage system nodes are highly dynamic. That nodes are from online to offline frequently will lead difficulty to system reliability analysis. If increasing the number of copies because nodes are temporarily offline, it will cause system to unnecessary outage. The larger number of copies will increase system reliability, but it will also cause the system to increase the cost of consistency maintenance. And the fewer number of copies will result in a significant reduction in reliability of the system.To address the problem of the quantity of copy and system reliability, a reliability model of P2P storage system which revolved around relationships between the rectuirements of data reliability measurement and the number of copies was built by stochastic Petri nets(SPN) and used to analysis. It identified the purpose and basic principles of studying system reliability from theory and can help to optimize the system design on curly stage.

Key words: Stochastic Petri ncts(SPN),P2P storage system, Reliability, Copy redundancy