The Calypso recovery scheme uses a protocol between the clients and servers, and it relies on the state distributed among clients. In the event of a server failure, multi-ported disks allow another processor to take over its disks and function as the file server. The advantages of the Calypso recovery scheme are that there is no need to explicitly replicate server state, and that the multi-ported disks shorten recovery times and offer cluster reorganization capability. AFS offers scalability but does not provide non-disruptive recovery. Several research distributed file systems demonstrated fault-tolerance using redundancy provided by replication and RAID techniques.
Recovery using distributed state avoids the expense of maintaining replicas.
Two other distributed file systems, Sprite and Spritely NFS have used distributed state for server recovery. Calypso development took place in parallel and independent of these efforts. Calypso differs from Sprite and Spritely NFS in state representation and internal design. Calypso implements failure detection, recovery management, and congestion control quite differently, and in separate subsystems with well-defined interfaces. The Calypso design also separates cache consistency state from file data, enhancing the modularity and further simplifying the recovery system.