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FACE: Enhancing Distributed File Systems for Autonomous Computing Environments

Report ID:
February 1989
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As distributed systems become larger, the appropriate system architectures are those that provide a great deal of support for local node autonomy. Since in such autonomous computing environments we expect that servers will have the freedom to deny service to any user, we believe that the proper view of
a server is not that it is the only place in which to obtain a service or resource, but rather a server is the best place to do so. In the case of CPU servers it is clear how the above may be accomplished: a job that is denied service at a server will simply be run locally, although perhaps in a degraded fashion. It is less clear what to do in the case of a file server. A possible approach consists of storing at the server the latest copy of all user files, while keeping local copies of older versions of the most crucial information. Thus, even after a failure users may be able to proceed with their work, although in a degraded manner. The idea of keeping local copies of key information has been called "stashing" in the literature. We augment
the usefulness of stashing by combining it with the idea of "quasi-copies" (remote data copies that are allowed to diverge from the primary data but in a controlled, application-dependent fashion), which eases the cost of maintaining replicated data. In this paper we present the design of FACE, a distributed
file system which allows users the option of using stashed files that are kept sufficiently consistent to fulfill user needs. The first FACE prototype has been designed and is currently being built via a series of enhancements to Sun's NFS.

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