CACHE COHERENCE IN DISTRIBUTED SYSTEMS (NETWORK, FILE SYSTEMS)

CHRISTOPHER ANGEL KENT, Purdue University

Abstract

Caching has long been recognized as a powerful performance enhancement technique in many areas of computer design. Most modern computer systems include a hardware cache between the processor and main memory, and many operating systems include a software cache between the file system routines and the disk hardware. In a distributed file system, where the file systems of several client machines are separated from the server backing store by a communications network, it is desirable to have a cache of recently used file blocks at the client, to avoid some of the communications overhead. In this configuration, special care must be taken to maintain consistency between the client caches, as some disk blocks may be in use by more than one client. For this reason, most current distributed file systems do not provide a cache at the client machine. Those systems that do place restrictions on the types of file blocks that may be shared, or require extra communication to confirm a cached block is still valid each time the block is to be used. The Caching Ring is a combination of an intelligent network interface and an efficient network protocol that allows caching of all types file blocks at the client machines. Blocks held in a client cache are guaranteed to be valid copies. We measure the style of use and performance improvement of caching in an existing file system, and develop the protocol and interface architecture of the Caching Ring. Using simulation, we study the performance of the Caching Ring and compare it to similar schemes using conventional network hardware.

Degree

Ph.D.

Subject Area

Computer science

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