Disconnected Operation in a Distributed File System

Disconnected Operation in a Distributed File System -...

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Unformatted text preview: Disconnected Operation in a Distributed File System James Jay Kistler May 1993 CMU-CS-93-156 School of Computer Science Carnegie Mellon University Pittsburgh, PA 15213 Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Thesis Committee: Mahadev Satyanarayanan, Chair Eric Cooper Richard Rashid Michael Schroeder, Digital Systems Research Center Copyright c 1993 James Jay Kistler This research was supported in part by an IBM Graduate Fellowship, in part by the National Science Foundation under Grant No. CCR-8657907, and in part by the Avionics Laboratory, Wright Research and Development Center, Aeronautical Systems Division (AFSC), U.S. Air Force, Wright-Patterson AFB, OH 45433-6543 under Contract F33615-90-C-1465, Arpa Order No. 7597. The views and conclusions contained in this document are those of the author and should not be interpreted as representing the official policies, either expressed or implied, of the IBM Corporation or the U.S. Government. Keywords: Disconnected operation, distributed file systems, high availability, mobile com-puters, caching, transparency, optimistic replication, hoarding, server emulation, reintegration, Coda. For Chris Abstract Disconnected operation refers to the ability of a distributed system client to operate despite server inaccessibility by emulating services locally. The capability to operate disconnected is already valuable in many systems, and its importance is growing with two major trends: the increasing scale of distributed systems, and the proliferation of powerful mobile computers. The former makes clients vulnerable to more frequent and less controllable system failures, and the latter introduces an important class of clients which are disconnected frequently and for long durationsoften as a matter of choice. This dissertation shows that it is practical to support disconnected operation for a fun-damental system service: general purpose file management. It describes the architecture, implementation, and evaluation of disconnected file service in the Coda file system. The ar-chitecture is centered on the idea that the disconnected service agent should be one and the same with the client cache manager. The Coda cache manager prepares for disconnection by pre-fetching and hoarding copies of critical files; while disconnected it logs all update activity and otherwise emulates server behavior; upon reconnection it reintegrates by sending its log to the server for replay. This design achieves the goal of high data availabilityusers can access many of their files while disconnected, but it does not sacrifice the other positive properties of contemporary distributed file systems: scalability, performance, security, and transparency....
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Disconnected Operation in a Distributed File System -...

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