Server recovery using naturally replicated state: a case study

This paper describes design and preliminary measurements of a file server recovery scheme that uses naturally replicated state among clients. This scheme, implemented in the Calypso file system, is truly transparent to the user and avoids the overhead of explicit replication. A three-phase protocol reconstructs the server state either on a backup node (if disks are multi-ported) or on the rebooted server node. Measurements show that the recovery time is about 21 seconds for a busy 10-node cluster. However, the time to rebuild the distributed state is only about 1.5 seconds, and most of the recovery time is spent in replaying the write-ahead log of the underlying file system. Fortunately, the log redo time is bounded by the log size.