Voting with Bystanders

Voting protocols ensure the consistency of replicated data objects by disallowing all read and write requests that cannot collect the appropriate quorum of replicas. Voting protocols require a minimum number of three copies to be of any practical use and often disallow a relatively high number of read and write requests. We present here a voting protocol overcoming this limitation and providing a significant amount of faulttolerance with as little as two replicas. Voting with Bystanders (VWB), as this protocol is named, applies to all networks consisting of LAN segments that are immune to partial failures linked by gateways that might fail. A stochastic analysis of the protocol under general Markovian assumptions is presented showing that VWB provides excellent read availabilities and good write availabilities with as little as two or three replicas.