Abstract- Coda is a file system for a large-scale distributed computing environment composed of Unix workstations. It provides resiliency to server and network failures through the use of two distinct but complementary mechanisms. One mechanism, server replication,stores copies of a file at multiple servers. The other mechanism, disconnected operation, is a mode of execution in which a caching site temporarily assumes the role of a replication site. Disconnected operation is particularly useful for supporting portable workstations. The design of Coda optimizes for availability and performance, and strives to provide the highest degree of consistency attainable in the light of these objectives. Measurements from a prototype show that the performance cost of providing high availability in Coda is reasonable. Index Terms- Andrew, availability, caching, disconnected operation, distributed file system, performance, portable computers, scalability, server replication. I.

The dissertation presents the issues addressed in the design of Ficus, a large scale wide area distributed file system currently operational on a modest scale at UCLA. Key aspects of providing such a service include toleration of partial operation in virtually all areas; support for large scale, optimistic data replication; and a flexible, extensible modular design. Ficus incorporates a "stackable layers" modular architecture and full support for optimistic replication. Replication is provided by a pair of layers operating in concert above a traditional filing service. A "volume" abstraction and on-the-fly volume "grafting" mechanism are used to manage the large scale file name space. The replication service uses a f...

This paper focuses on the mechanisms in Coda to cope with conflicts and describes our experience in implementing them. Other aspects of Coda are described in earlier papers [3, 4]. 2. Support for Optimistic Replication In a system that adopts an optimistic replication strategy there must be support to cope with conflicts when they arise. Specifically the system should: ffl be able to detect a conflict as soon as possible after it arises, 1

Management of related, replicated objects is often fundamental to the design of reliable distributed systems. We are concerned both with the objects themselves: propagation of updates and reclamation of storage; as well as management of the possibly replicated directories used to keep track of and find the objects. This paper presents a family of algorithms for use in managing replicated objects and the accompanying graph structured directory systems. Members of this family are presented in order of increasing power and flexibility, followed by discussion of their correctness. The use of the algorithms in a replicated file system context is outlined throughout the presentation. 1 Introduction Desires to improve availability and performance of information serves to motivate replicating information at locations "closer" to the data's intended This work was sponsored by DARPA under contract number F29601-87-C-0072. y This author is also affiliated with Locus Computing Corporation. u...

Coda is a file system for a large-scale distributed computing environment composed of Unix workstations. It pro- vides resiliency to server and network failures through the use of two distinct but complementary mechanisms. One mechanism, server replication,stores copies of a file at multiple servers. The other mechanism, disconnected operation, is a mode of execution in which a caching site temporarily assumes the role of a replication site. Disconnected operation is particularly useful for supporting portable workstations. The design of Coda optimizes for availability and performance, and strives to provide the highest degree of consistency attainable in the light of these objectives. Measurements from a prototype show that the performance cost of providing high availability in Coda is reasonable. Index Terms- Andrew, availability, caching, disconnected operation, distributed file system, performance, portable computers, scalability, server replication. I. INTRODUCTION LOCATION-t...

This paper focuses on the mechanisms in Coda to cope with conflicts and describes our experience in implementing them. Other aspects of Coda are described in earlier papers [3, 4].