Management

• PC-NFS/DOS file systems. These will be essential for safe software availability (since distribution to pure DOS machines could be a disaster area). Probably best not to allow DOS machines to hold user files if possible.
• Andrew AFS - a vastly superior distributed file system to NFS, but not in widespread use. Mentioned as favoured in the Decorum proposal. Probably ideal for teaching since chached files used in teaching are relatively small. Known to co-exist with NFS. How it interacts with naming/mounting/access control not known.
• The CODA file system extends the AFS (see later) to add cache coherence algorithm. Basically, a CODA client has a cache of a file. Since most files are read only, network partitioning or even server crash are not a problem. If a client opens a file for write, CODA is optimistic, and simply assumes that statistically, it is unlikely two clients will open the same file to write. If they do, then on writing the cache back to the server there is a roll-back, and re-integration scheme that is invoked. Unfortunately, for many common filesystems, a file is a stream of bytes (c.f. Unix/DOS), and integration of two sequences of changes is not meaningful. This has led to the next generation of filesystem designs, where all files are kept in a series of updates of their contents. With decreasing storage costs, such <#2401#> Log Structured Filesystems<#2401#> are becoming increasingly attractive, since they simplify a number of error recovery procedures outside distributed systems as well as inside.