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In this paper, we consider the performance of alternative mass storage services for a client-server style distributed system. Some qualitative arguments are presented on the ramifications of implementations of mass storage services at various levels of the storage semantics hierarchy. This paper concentrates, in particular, on contrasting disk and files services. The functionality of disk and file services are distinguished by their primitive operations: individual disk block access, for the disk service; and individual file block access, for the file service. This difference results in different partitionings of the computation between the client and server, as well as different network communication requirements. To understand the ramifications of such differences between the services, this paper presents performance estimates for basic disk and file services. To provide a commensurate comparison of the performance of the two services, a uniform closed queueing network model was developed that accurately portrayed this computation/communication tradeoff. Detailed parameterization of the model was done through measurements of prototype systems. The workload applied to the mass storage service is based on measurements of timesharing systems performed in earlier studies. In addition to the basic comparisons, performance estimates for several design alternatives are also presented. Some of these performance enhancing alternatives were: caching of file/disk blocks and file-opens, kernel-based services, and using a network interface able to do gather write to eliminate data copies. [ABSTRACT FROM AUTHOR]