A Toolkit Approach to Partially Connected Operation
Dan Duchamp
Columbia University and AT&T Labs
Abstract
Partially connected operation is the circumstance in which the
communication link between two computers is intermittent, either by
choice or because of failure. This paper describes the design and
performance of a user level toolkit that is suited to accessing the home
directory of a partially connected user in a bandwidth-efficient manner.
Compared to custom file systems for partially connected operation,
the toolkit is easier to deploy and provides extra degrees of
flexibility because it runs at user level and uses the local file system
for its cache. The toolkit makes it possible for unaltered clients to
access NFS file systems exported by unaltered servers.
The
maintenance of consistency between client and server is automatic
provided that certain assumptions are upheld, the primary one being that
sharing is limited in such a way that there is a "single locus of
update." That is, for extended periods, updates are applied either to
the client's cache or directly to the server, but not to both
simultaneously. This pattern of use is typical of a user's home
directory.
Performance is the disadvantage of user level operation.
The client's cache is managed by a "caching tool" that services every
file system operation and this redirection increases latency
substantially.
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