The effect of client caching on file server workloads

A distributed file system provides a file service from one or more shared file servers to a community of client workstations over a network. While the client-server paradigm has many advantages, it also presents new challenges to system designers concerning performance and reliability. As both client workstations and file servers become increasingly well-resourced, a number of system design decision need to be re-examined. This research concerns the caching of disk-blocks in a distributed client-server environment. Some recent research has suggested that various strategies for cache management may not be equally suited to the circumstances at both the client and the server. Since any caching strategy is based on assumptions concerning the characteristics of the demand, the performance of the strategy is only as good as the accuracy of this assumption. The performance of a caching strategy at a file server is strongly influenced by the presence of client caches since these caches alter the characteristics of the stream of requests that reaches the server. This paper presents the results of an investigation of the effect of client caching on the nature of the server workload as a step towards understanding the performance of caching strategies at the server. The results demonstrate that client caches alter workload characteristics in a way that leaves a profound impact on server cache performance, and suggest worthwhile directions for the future development of server caching strategies.