Augmenting Availability in Distributed File Systems
A very important feature in distributed systems is the availability of the services offered by the system. Traditionally, distributed systems provide the services by centralizing their administration at remote servers. This leaves the door open for increased dependency on these servers and the network connecting them to the local facilities. This may be a problem in environments where availability is a concern, e.g., very large distributed systems. In this paper, we describe the design of a distributed file system called FACE, that uses the notions of stashing (keeping local copies of key information) and quasi-copies (data copies that are allowed to diverge from the primary data but in a controlled, application-dependent fashion), to augment the availability of crucial files even when the file server that contains them is no longer reachable. We also report on the first FACE prototype that has been designed and implemented via a series of enhancements to Sun's Network File System.