Coda: a highly available file system for a distributed workstation environment

A description is given of Coda, a file system for a large-scale distributed computing environment composed of Unix workstations. It provides resilience to server and network failures through the use of two distinct but complementary mechanisms. One mechanism, server replication, involves storing copies of a file at multiple servers. The other mechanism, disconnected operation, is a mode of execution in which a caching site temporarily assumes the role of a replication site. Disconnected operation is particularly useful for supporting portable workstations. The design of Coda optimizes availability and performance and provides the highest degree of consistency attainable. Measurements from a prototype show that the performance cost of providing high availability in Coda is reasonable