Replication Degree Customization for High Availability
Practice talk for Eurosys 2008. http://www.dcs.gla.ac.uk/Conferences/EuroSys2008/
Object replication is a common approach to enhance the
availability of distributed data-intensive services and stor
age systems. Many such systems are known to have highly
skewed object request probability distributions. In this pa-
per, we propose an object replication degree customization
scheme that maximizes the expected service availability under given object request probabilities, object sizes, and space constraints (e.g., memory/storage capacities). In particular, we discover that the optimal replication degree of an object should be linear in the logarithm of its popularity-to-size ratio. We also study the feasibility and effectiveness of our proposed scheme using applications driven by real-life system object request traces and machine failure traces. When the data object popularity distribution is known a priori, our proposed customization can achieve 1.322.92 "nines" increase in system availability (or 2174% space savings at the same availability level) compared to uniform replication. Results also suggest that our scheme requires a moderate amount of replica creation/removal overhead (weekly changes involve no more than 0.24% objects and no more than 0.11% of total data size) under realistic object request popularity changes.