Extended file system on UNIX 4.2/4.3 BSD

[Doug Gwyn <gwyn>]

> ATT/RFS implements unix file system semantics exactly at the expense of not
> being stateless and not caching data in the client.  NFS has a stateless
> server at the expense of unix file system semantics.  In case it isn't
> obvious, the big advantage of a stateless server is that it simplifies
> recovery after machine or network failure.

AT&T's RFS, I was told, treats a network link going down the same
as it would a disk going off-line; there will be an error returned
from any subsequent attempt to do I/O to the inaccessible file.

Note that full support for UNIX file system semantics is a crucial
issue for AT&T UNIX System V systems, which support record locking.

The obvious alternative to I/O errors when a net link goes down is
to block processes doing remote file I/O over the link until it
comes back up; this is probably unwise for record locking systems.