Using stashing to increase node autonomy in distributed file systems

The authors present an enhancement to distributed file systems that allows the users of the system to keep local copies of important files, decreasing the dependency over file servers. Using the notions of stashing and quasi-copies, the system allows users to tune up the quality of the service they want to receive when the file server is not reachable. One of the key points of this work is the focus on the tradeoff between availability and degradation of service. The other main contribution is the design of a distributed file system which is ideally suited to very large distributed systems, in that it provides users with greater tolerance of network partitions and server failures. It is emphasized that the use of stashing does not preclude the use of other performance-enhancing or fault-tolerant techniques. The file system architecture has been implemented and FACE, a prototype of a file system service based on Sun´s NFS, is described. Performance figures are reported. These figures show that the overhead of providing the service is negligible. Current plans also call for porting the FACE design to a number of other processors