Path: utzoo!mnetor!uunet!husc6!mailrus!nrl-cmf!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!hplabs!hp-pcd!uoregon!jqj
From: jqj@uoregon.UUCP (JQ Johnson)
Newsgroups: comp.dcom.lans
Subject: Re: NFS vs RFS (actually, vs Sprite and Andrew)
Message-ID: <1695@uoregon.UUCP>
Date: 15 Mar 88 06:39:54 GMT
References: <10370@ut-sally.UUCP> <720@uel.uel.co.uk>
Reply-To: jqj@drizzle.UUCP (JQ Johnson)
Organization: University of Oregon, Computer Science, Eugene OR
Lines: 30
Keywords: NFS, ANDREW, TOCS, consistency

The latest issue of TOCS (Feb. 1988) contains 2 papers from the 1987
SIGOPS Symposium that are directly relevant to a comparison of network
file systems.  A paper by John Howard et al discusses the VICE system
(part of the C-MU Andrew project), and a paper by Nelson et al discusses
Sprite, a network file system being developed at Berkeley.  Both papers
compare their system with SUN NFS, arguing that NFS is perceived as "a
de facto standard" but that it has serious deficiencies when compared
to their preferred system.

Problems sited with NFS seem to fall into 2 categories:
1/	scalability to large systems, because of excessive network
	traffic, excessive server cpu loading, or difficulty in 
	administration;
2/	problems with consistency semantics.  For example, under
	SUN NFS if processes on different workstations perform
	interleaved write to a file the result is indeterminate.
The two problems are argued to be related; since NFS is stateless the
server cannot use any knowledge of client file caching, and hence
caching must be minimized to insure consistency (that's my interpretation
of the papers, not necessarily the authors').

Since these papers have been floating around for almost a year, I would
think that by now SUN would have a response, either in the form of counter-
arguments or draft revisions to the NFS spec.  Would someone from SUN
care to comment?

I am particularly concerned by the difficulty in formally describing
the consistency semantics of NFS.  Granted that NFS is designed to
work right "most of the time", it is troubling to be unable to reason
formally about distributed systems built on top of NFS.