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Replication for Mobile Computers

The Travler project is working on several mobile data replication services. The most mature is Rumor.

Rumor is a file replication system that can be used to keep multiple copies of files consistent. Rumor is especially useful for keeping replicated files on mobile computers. Maintaining multiple replicas of each file allows for higher availability. In particular, allowing mobile computers to store file replicas ensures that they will be able to access important data while disconnected, while still maintaining a single environment shared with workstation machines when connected. To further improve availability, Rumor uses an optimistic replication strategy. Optimistic replication permits any accessible replica to be updated, thus allowing disconnected portable computers to not only read, but also write, their local file replicas.

The Rumor icon appears here. Rumor is a portable optimistic replicated file service built as a wrapper around an existing file system. We have a Linux version of Rumor up and running, with a beta release available on the web. Rumor portability is achieved by dividing the system's functionality into a larger system independent replication service and a smaller system dependent service.

Rumor uses important algorithms and data structures originally built for Ficus. Ficus is a successful in-kernel replication service based on SunOS 4.1.1.

The Ficus icon appears here.

Since Rumor is a user-level system, it can be installed and maintained by normal users. No root privileges are required.

Rumor's optimistic replication strategy will permit concurrent updates, which can lead to inconsistent replicas of a single file. Rumor detects such inconsistencies and applies automated mechanisms to resolve them.

We are currently working on other replication solutions to mobile computing problems, including a file hoarding service for portable computers Seer and a file replication service capable of supporting hundreds of writable replicas.

A position paper on Rumor was presented in the SIGCOMM Workshop on Middleware.

If you have any questions or comments about Rumor, please contact the development team.

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Last modified: Tue Mar 3 09:50:32 PST 1998