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Replicating a data object improves the availability of the data, and can improve access latency by locating copies of the object near to their use. When accessing replicated objects across an internetwork, the time to access different replicas is non-uniform.

File systems provide an interface for applications to obtain exclusive access to files, in which a process holds privileges to a file that cannot be preempted and restrict the capabilities of other processes. Local file systems do this by maintaining information about the privileges of current file sessions, and checking subsequent sessions for compatibility.

In a distributed system, data are often replicated for protection against site failures and network partitions. Through the use of replication, increased availability of data and reliability of access can be obtained.

We investigate the construction of a reliable device. Such a device appears to the file system as an ordinary block-structured device, but is implemented as a set of server processes on several sites.