Stochastic Petri net analysis of a replicated file system

The authors present a stochastic Petri net model of a replicated file system in a distributed environment where replicated files reside on different hosts and a voting algorithm is used to maintain consistency. Witnesses, which simply record the status of the file but contain no data, can be used in addition to or in place of files to reduce overhead. A model sufficiently detailed to include file status (current or out-of-date) as well as failure and repair of hosts where copies or witnesses reside, is presented. The number of copies and witnesses is not fixed, but is a parameter of the model. Two different majority protocols are examined.<>