A Toolkit Approach to Partially Connected Computing

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.