This research proposes and tests an approach to engineering distributed file systems that are aimed at wide-scale, Internet-based use. The premise is that replication is essential to deliver performance and availability, yet the traditional conservative replica consistency algorithms do not scale to this environment. Our Ficus replicated file system uses a single-copy availability, optimistic update policy with reconciliation algorithms that reliably detect concurrent updates and automatically restore the consistency of directory replicas. The system uses the peer-to-peer model in which all machines are architectural equals but still permits configuration in a client-server arrangement where appropriate. Ficus has been used for six years at several geographically scattered installations. This paper details and evaluates the use of optimistic replica consistency, automatic update conflict detection and repair, the peer-to-peer (as opposed to client-server) interaction model, and the stackable file system architecture in the design and construction of Ficus. The paper concludes with a number of lessons learned from the experience of designing, building, measuring, and living with an optimistically replicated file system. © 1998 John Wiley & Sons, Ltd.

This paper presents a practical set of algorithms for maintaining the consistency of a replicated file system with an optimistic update policy. These algorithms permit a system which allows updates to an object so long as any copy is available; the algorithms then return the various copies to consistency at their first opportunity. These algorithms have been used to build the Ficus replicated file system.>

Many tools and techniques exist for the modeling and analysis of computer and communication systems. These tools are often complex and tailored to a narrow range of problems. The system analysis task often requires coordinated use of multiple tools and techniques which is not supported by currently available systems. The Tangram project goal is to develop an environment which makes a large set of tools and techniques readily accessible and is easily tailored to specialized applications.

An approach to the architecture of distributed databases is presented, oriented around extensive embeddmg of database prinntives in the underlying distributed operating system.It is shown that this approach greatly reduces the effort required to provide high quality distributed database services.Substantial portions of this approach are implemented and are operational as extensions to the Locus distributed Unix operating system.TIns paper describes the approach, compares it with other work, argues why rt is attractive and what drawbacks are present, and lays out what has been done and what remains.