FAST 2002 Abstract
Safety, Visibility, and Performance in a Wide-Area File System
Minkyong Kim, Landon P. Cox, and Brian D. Noble, Electrical Engineering and Computer Science
University of Michigan
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
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, pre-serving
common case performance. Furthermore, the benefits
of independent update outweigh the costs of sharing for a work load
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.
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