Discovery and Hot Replacement of Replicated Read-Only File Systems,
with Application to Mobile Computing
Erez Zadok and Dan Duchamp
Computer Science Department
We describe a mechanism for replacing files, including open files, of
a read-only file system while the file system remains mounted; the act
of replacement is transparent to the user. Such a "hot replacement"
mechanism can improve fault-tolerance, performance, or both. Our
mechanism monitors, from the client side, the latency of operations
directed at each file system. When latency degrades, the client
automatically seeks a replacement file system that is equivalent to
but hopefully faster than the current file system. The files in the
replacement file system then take the place of those in the current
file system. This work has particular relevance to mobile computers,
which in some cases might move over a wide area. Wide area movement
can be expected to lead to highly variable response time, and give
rise to three sorts of problems: increased latency, increased
failures, and decreased scalability. If a mobile client moves through
regions having partial replicas of common file systems, then the
mobile client can depend on our mechanism to provide increased fault
tolerance and more uniform performance.
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