On Correlated Failures in Survivable Storage Systems (CMU-CS-02-129)

The design of survivable storage systems involves inherent trade-offs among properties such as performance, security, and availability. A toolbox of simple and accurate models of these properties allows a designer to make informed decisions. This report focuses on availability modeling. We describe two ways of extending the classic model of availability with a single “correlation parameter” to accommodate correlated failures. We evaluate the efficacy of the models by comparing their results with real measurements. We also show the use of the models as design decision tools: we analyze the effects of availability and correlation on the ordering of data distribution schemes and we investigate the placement of related files. Acknowledgements: This work is partially funded by DARPA/ITO’s Organically Assured and Survivable Information Systems (OASIS) Program (Air Force contract number F30602-99-2-0539-AFRL). We thank the members and companies of the PDL Consortium (including EMC, HP, Hitachi, IBM, Intel, Network Appliance, Panasas, Seagate, Sun and Veritas) for their interest, insights and support. We also thank Microsoft Corporation for sharing their availability measurements of the desktops in their campus.