On Improving the Availability of Replicated Files
To improve the availability and reliability of les the data are often replicated at several sites. A scheme must then be chosen to maintain the consistency of the le contents in the presence of site failures. The most commonly used scheme is voting. Voting is popular because it is simple and robust: Voting schemes do not depend on any sophisticated message passing scheme and are unaffected by network partitions. When network partitions cannot occur, better availabilities and reliabilities can be achieved with the available copy scheme. This scheme is somewhat more complex than voting as the recovery algorithm invoked after a failure of all sites has to know which site failed last.