Safety, visibility, and performance in a wide-area file system

  • Authors:

  • Minkyong Kim;Landon P. Cox;Brian D. Noble

  • Affiliations:

  • Electrical Engineering and Computer Science, University of Michigan;Electrical Engineering and Computer Science, University of Michigan;Electrical Engineering and Computer Science, University of Michigan

  • Venue:
  • FAST'02 Proceedings of the 1st USENIX conference on File and storage technologies
  • Year:
  • 2002

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Abstract

As mobile clients travel, their costs to reach home filing services change, with serious performance implications. Current file systems mask these performance problems by reducing the safety of updates, their visibility, or both. This is the result of combining the propagation and notification of updates from clients to servers. Fluid Replication separates these mechanisms. Client updates are shipped to nearby replicas, called WayStations, rather than remote servers, providing inexpensive safety. WayStations and servers periodically exchange knowledge of updates through reconciliation, providing a tight bound on the time until updates are visible. Reconciliation is non-blocking, and update contents are not propagated immediately; propagation is deferred to take advantage of the low incidence of sharing in file systems. Our measurements of a Fluid Replication prototype show that update performance is completely independent of wide-area networking costs, at the expense of increased sharing costs. This places the costs of sharing on those who require it, preserving common case performance. Furthermore, the benefits of independent update outweigh the costs of sharing for a workload with substantial sharing. A trace-based simulation shows that a modest reconciliation interval of 15 seconds can eliminate 98% of all stale accesses. Furthermore, our traced clients could collectively expect availability of five nines, even with deferred propagation of updates.