A new file system for mobile computing.

摘要

The recent proliferation of portable computers, the introduction of a variety of pocket-sized computing devices and the rapid expansion of computer networks provide great promise for a future in which mobility of both users and computers will be standard. However, these developments also invalidate many of the assumptions made by current system software, which was designed for stationary systems and users.; An important component of system software that needs redesign for mobility is the file system. Ideally, a user should be able to access the files he or she needs regardless of location. Although existing distributed file systems such as Coda provide a partial solution by supporting disconnected operation of clients, significant deficiencies remain. For example, the distributed file system is unavailable at isolated computers. This work argues that the limited availability results from the strict client-server model used and proposes a looser model.; A design based on this relaxed model is presented. It utilizes a persona carrier, a computer that accompanies its owner at all times, as the bridge between isolated computers and servers. The persona carrier acts as a regular client when connected, hoarding files from servers. When disconnected, it may be used independently or as a pseudo-server to an isolated computer, providing it with needed files and recording any updates made there. Upon reconnection, the persona carrier propagates these updates to the servers.; A prototype implementation has been built successfully, thereby demonstrating the viability and usefulness of the proposed design. It uses Coda as the distributed file system. The Coda client has been modified to allow it to act as a pseudo-server to an isolated computer. It has also been modified for use on an isolated computer, as a client of a persona carrier. An evaluation of the prototype indicates that Coda access at the isolated computer resembles that at a regular connected client in both feel and performance.