The Andrew File System is a location-transparent distributed tile system that will eventually span more than 5000 workstations at Carnegie Mellon University. Large scale affects performance and complicates system operation. In this paper we present observations of a prototype implementation, motivate changes in the areas of cache validation, server process structure, name translation, and low-level storage representation, and quantitatively demonstrate Andrew’s ability to scale gracefully. We establish the importance of whole-file transfer and caching in Andrew by comparing its perform-ance with that of Sun Microsystem’s NFS tile system. We also show how the aggregation of files into volumes improves the operability of the system.

Mobile clients face wide variations in network conditions and local resource availability when accessing remote data. Coping with this uncertainty requires the ability to retrieve and present data at varying degrees of fidelity. In this paper we present applicaton-aware adaptation as a solution to this problem. The essence of our solution is a collaborative partnership between applications and the operating system. We describe the Odyssey API for application-aware adaptation and demonstrate its use in accessing two types of data: video and maps.

Andrew is a distributed computing environment that is a synthesis of the personal computing and timesharing paradigms. When mature, it is expected to encompass over 5,000 workstations spanning the Carnegie Mellon University campus. This paper examines the security issues that arise in such an environment and describes the mechanisms that have been developed to address them. These mechanisms include the logical and physical separation of servers and clients, support for secure communication at the remote procedure call level, a distributed authentication service, a file-protection scheme that combines access lists with UNIX mode bits, and the use of encryption as a basic building block. The paper also discusses the assumptions underlying security in Andrew and analyzes the vulnerability of the system. Usage experience reveals that resource control, particularly of workstation CPU cycles, is more important than originally anticipated and that the mechanisms available to address this issue are rudimentary.

The purpose of a distributed file system (DFS) is to allow users of physically distributed computers to share data and storage resources by using a common file system. A typical configuration for a DFS is a collection of workstations and mainframes connected by a local area network (LAN). A DFS is implemented as part of the operating system of each of the connected computers. This paper establishes a viewpoint that emphasizes the dispersed structure and decentralization of both data and control in the design of such systems. It defines the concepts of transparency, fault tolerance, and scalability and discusses them in the context of DFSs. The paper claims that the principle of distributed operation is fundamental for a fault tolerant and scalable DFS design. It also presents alternatives for the semantics of sharing and methods for providing access to remote files. A survey of contemporary UNIX@-based systems, namely, UNIX United, Locus, Sprite, Sun’s Network File System, and ITC’s Andrew, illustrates the concepts and demonstrates various implementations and design alternatives. Based on the assessment of these systems, the paper makes the point that a departure from the approach of extending centralized file systems over a communication network is necessary to accomplish sound distributed file system design.

AFS plays a prominent role in our plans for a mobile workstation. The AFS client manages a cache of the most recently used files and directories. But even when the cache is hot, access to cached data frequently involves some communication with one or more file servers to maintain consistency guarantees. Without network access, cached data is soon rendered unavailable. We have modified the AFS cache manager to offer optimistic consistency guarantees when it can not communicate with a file server. When the client reestablishes a connection with the file server, it tries to propagate all file modifications to the server. If conflicts are detected, the replay agent notifies the user that manual resolution is needed. Our system brings the benefits of contemporary distributed computing environments to mobile laptops, offering a fresh look at the potential for nomadic computing.

JetFile is a file system designed with multicast as its distribution mechanism. The goal is to support a large number of clients in an environment such as the Internet where hosts are attached to both high and low speed networks, sometimes over long distances. JetFile is designed for reduced reliance on servers by allowing client-to-client updates using scalable reliable multicast. Clients on high speed networks prefetch large numbers of files. On low speed networks such as wireless, special caching policies are used to decrease file access latency. The prototype implementation of JetFile is on the JetStream gigabit local area network which provides hardware support for many multicast addresses. The multicast Internet backbone (Mbone) is the wide area testbed for JetFile. 1 Introduction To achieve scalability in a wide area network environment, the next generation of distributed file systems need a new paradigm of communication. The prevailing mode of communication for current distrib...

Abstract This paper is a survey of the current state of the art in the design and implementation of distributed file systems. It consists of four major parts: an overview of background material, case studies of a number of contemporary file systems, identification of key design techniques, and an examination of current research issues. The systems surveyed are Sun NFS, Apollo Domain, Andrew, IBM AIX DS, AT&T RFS, and Sprite. The coverage of background material includes a taxonomy of file system issues, a brief history of distributed file systems, and a summary of empirical research on file properties. A comprehensive bibliography forms an important of the paper. Copyright (C) 1988,1989 M. Satyanarayanan The author was supported in the writing of this paper by the National Science Foundation (Contract No. CCR-8657907), Defense Advanced Research Projects Agency (Order No. 4976, Contract F33615-84-K-1520) and the IBM Corporation (Faculty Development Award). The views and conclusions in t...

The evolution of the Andrew File System (AFS) into a wide-area distributed file system has encouraged collaboration and information dissemination on a much broader scale than ever before. In this paper, we examine AFS as a provider of wide-area file services to over a hundred organizations around the world. We discuss usage characteristics of AFS derived from empirical measurements of the system. Our observations indicate that AFS provides robust and efficient data access in its current configuration, thus confirming its viability as a design point for widearea distributed file systems.

To function in mobile computing environments, distributed file systems must cope with networks that are slow, intermittent, or both. Intermittence vitiates the effectiveness of callback-based cache coherence schemes in reducing client-server communication, because clients must validate files when connections are reestablished. In this paper we show how maintaining cache coherence at a large granularity alleviates this problem. We report on the implementation and performance of large granularity cache coherence for the Coda File System. Our measurements confirm the value of this technique. At 9.6 Kbps, this technique takes only 4 – 20 % of the time required by two other strategies to validate the cache for a sample of Coda users. Even at this speed, the network is effectively eliminated as the bottleneck for cache validation.

In this paper we present results from a six-month empirical study of the high availability aspectsof the Coda File System. We report on the service failures experienced by Coda clients, and show that such failures are masked successfully. We also explorethe effectiveness and resource costs of key aspects of server replication and disconnected operation, the two high availability mechanisms of Coda. Wherever possible, we compare our measurements to simulation-based predictions from earlier papers and to anecdotal evidence from users. Finally, we explore how users take advantage of the support provided by Coda for mobile computing.