Exploiting Weak Connectivity in a Distributed File System.

Abstract

Weak connectivity, in the form of intermittent, low-bandwidth, or expensive networks is a fact of life in mobile computing. For the foreseeable future, access to cheap, high-performance, reliable networks, or strong connectivity will be limited to a few oases, such as work or home, in a vast desert of weak connectivity. The design of distributed file systems has traditionally been based on an assumption of strong connectivity. Yet, to provide ubiquitous data access, it is vital that distributed file systems make effective use of weak connectivity. This dissertation describes the design, implementation, and evaluation of weakly connected operation in the Coda File System. The starting point of this work is disconnected operation, in which a file system client operates using data in its cache during server or network failures. Disconnected clients suffer from many limitations: updates are not visible to other clients, cache misses may impede progress, updates are at risk from client loss or damage, and the danger of update conflicts increases as disconnections are prolonged. Weak connectivity provides an opportunity to alleviate these limitations. Coda's strategy for weakly connected operation is best characterized as application-transparent adaptation. The system bears full responsibility for coping with the demands of weak connectivity. This approach preserves upward compatibility by allowing applications to run unchanged. Coda provides several mechanisms for weakly connected operation motivated by actual experience. The foundation of adaptivity in this system is the communications layer, which derives and supplies information on network conditions to higher system layers. The rapid cache validation mechanism enables the system to recover quickly in intermittent environments.

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Document Details

Document Type
Technical Report
Publication Date
Dec 01, 1996
Accession Number
ADA322734

Entities

People

  • Lily B. Mummert

Organizations

  • Carnegie Mellon University

Tags

Communities of Interest

  • Energy and Power Technologies
  • Engineered Resilient Systems
  • Ground and Sea Platforms

DTIC Thesaurus Topics

  • Application Protocols
  • Authentication
  • Circuit Boards
  • Computer Programming
  • Computers
  • Data Compression
  • Data Transmission
  • Debugging
  • Electronic Mail
  • Failure Mode And Effect Analysis
  • Local Area Networks
  • Network Science
  • Operating Systems
  • Reliability
  • Transport Protocols
  • Web Browsers
  • Wireless Communications

Fields of Study

  • Computer science

Readers

  • Mathematical Modeling and Probability Theory.
  • Parallel and Distributed Computing.