A comparison of two approaches to build reliable distributed file servers

Several existing distributed file systems provide reliability by server replication. An alternative approach is to use dual-ported disks accessible to a server and a backup. The two approaches are compared by examining an example of each. Deceit is a replicated file server that emphasizes flexibility. HA-NFS is an example of the second approach that emphasizes efficiency and simplicity. The two file servers run on the same hardware and implement SUN´s NFS protocol. The comparison shows that replicated servers are more flexible and tolerant of a wider variety of faults. On the other hand, the dual-ported disks approach is more efficient and simpler to implement. When tolerating single failure, dual-ported disks also give somewhat better availability