The Effect of Client Caching on File Server Workloads

A distributed file systetn provides file service from one or rnore &red file servers to a community of clierit workstations o’ver Q network. Wlaile the clientserver paradigm has many advantages, it also presents new challenges to system designers concerning perforrnance and reliability. As both client workstations and file servers become increasingly well-resourced, a nu~nber of system design decisions need to be re-examined. This research concerus the caching of disk blocks in a distributed client-server enviromnent. Some recent research has suggested that various strategies for cache rnauagernent may not be equally suited to the circurnstances at both the client and the server. Since any caching strategy is based on assumptions concerning the characteristics of the denland, the performance of the strategy is only as good as the accuracy of this assurnption. The perfornlance of a caching strategy at a file server is strongly influenced by the presence of client cnches 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 performnnce of caching strategies at the server. The results demonstrate that client caches alter worklond characteristics in a way that will have CI profound impact on server cnche perforrnance, and suggest worthwhile directions for future development of server caching strategies.