Reliability of replicated data objects

When fault tolerance is improved by replicating data at several sites, a protocol is required to maintain the consistency of the data object in the presence of site failures. The most commonly used scheme is voting, which is unaffected by network partitions. When network partitions cannot occur, better performance can be achieved with available copy protocols. The authors investigate the reliability of replicated data objects managed by voting, available copy, and their variants. Where possible, closed-form expressions for the reliability of the various consistency protocols are derived using standard Markovian assumptions. In other cases, numerical solutions are found and validated with simulation results.<>