SRC Research Report 46
SRC Research Report 46
Replication is an important technique for increasing computer system availability. In this paper, we present an algorithm for replicating stored data on multiple server machines. The algorithm organizes the replicated servers in a master/slaves scheme, with one master election being performed at the beginning of each service period. The status of each replica is summarized by a set of monotonically increasing epoch variables. Examining the epoch variables of a majority of the replicas reveals which replicas have up-to-date data. The set of replicas can be changed dynamically. Replicas that have been off-line can be brought up to date in background, and witness replicas, which store the epoch variables but not the data, can participate in the majority voting. The algorithm does not require distributed atomic transactions. The algorithm also permits client machines to cache copies of data, with strict cache consistency being ensured by having the replicated servers keep track of which clients have cached what data. The work reported in this paper is part of an ongoing project to build a new replicated distributed file system with client caching, called Echo.
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