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CURRENT_MEETING_REPORT_
Reported by Peter Honeyman/UMICH
Minutes of the Distributed File System Working Group (DFS)
The DFS Working Group met for the third time on November 19, 1991 at the
Santa Fe IETF.
Agenda
o NFS developments
o AFS-3 documents
o AFS-3 congestion control
o Announcements
NFS Developments
Tom Kessler (tom.kessler@eng.sun.com) described work at Sun to add local
disk caching to NFS.
The Cache File System (CFS) is a generic mechanism that caches files and
directories from other VFS systems. The principal cache repository is
UFS, i.e., the Berkeley FFS.
A principal design goal to boost NFS server performance by reducing
load, but CFS helps reduce network load as well if the cache hit rate is
high. CFS is also useful for improving CD-ROM performance.
Like AFS-3, CFS caches chunks of files. Unlike AFS-3, there is a
one-to-one correspondence between cached files and files on the server.
Missing chunks are represented by ``holes'' in the cached file.
Consistency checking has not been implemented; CFS is a client-only
modification, so the consistency checking can be no stronger than that
in the VFS system being cached. The consistency check mechanism is
modular and offers hooks for a CFS developer to provide alternate
enforcement mechanisms.
``Blot-out'' mode lets you overlay files with local copies. The unit of
blot-out is a complete file. The local overlay is not purged from the
cache by ordinary LRU replacement policy. Other files can be marked to
make them ``sticky'' in the cache.
CFS supports numerous write modes:
o Write-through. Synchronous with server.
o Blot-out. Write to cache only, make local copy sticky. Useful for
writing CD-ROM.
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o Write-around. Modify actual file only. Useful if cache is scarce
resource. [I may not have this right.]
Write-through is the normal mode. CFS helps READ, READDIR, READLINK,
LOOKUP performance, does not help GETATTR, directory modifications,
WRITE, SETATTR.
As for the bottom line, Tom, who uses CFS on his home computer, was
asked ``How does it feel?'' According to Tom, ``It feels pretty good.''
Chris Silveri's foils, which Tom used in his CFS presentation, can be
obtained in PostScript form via anonymous FTP from citi.umich.edu. See
/afs/umich.edu/user/h/o/honey/IETF/cfs-vg.ps.
Other NFS Developments
There has been some progress on the part of vendors in tuning the NFS
parameters (tsize, RTO, RTT measurements) in systems they ship to better
conserve network resources. A number of people reported that they find
NFS/UDP over the Internet satisfactory. [At least one person was
surprised to hear this.]
NFS/TCP is commercially available, and is under development by many
vendors. Connection maintenance is not entirely a solved problem.
Sun/RPC over UDP has problems with accurate RTT because the network
latency is smeared by the upper-layer (i.e., NFS) service times. (See
``Transport Issues in the Network File System'' by Bill Nowicki,
Computer Communication Review 19(2), pp. 16-20 (April, 1989) for
related work.)
Watch Connectathon for further activity in the NFS/TCP arena.
AFS-3 Documents
There was some discussion of the four-or-so inches of AFS-3 documents
made available by Transarc. It is not clear what advantage there is in
putting an RFC imprimatur on them. Nor is Transarc enthusiastic about
reformatting the documents to conform to RFC 1111.
AFS-3 Congestion Control
Peter Honeyman (honey@citi.umich.edu) described his recent work on
congestion control for Rx. (Joint work with Dave Bachmann and Larry
Huston.) The goal has been to make AFS usable over slow links, down to
about 10 Kbits/sec. Much has been accomplished so far, work continues.
Announcements
dfs-wg@citi.umich.edu is a mailing list for ongoing discussions of the
Working Group. Administrative matters, such as requests to be added or
dropped from the list, should be addressed to
dfs-wg-request@citi.umich.edu, not to the list as a whole.
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There is a forthcoming Workshop on File Systems to be held in Ann Arbor
on May 21-22, 1992. Contact fsworkshop@citi.umich.edu for further
information.
Attendees
Mary Artibee artibee@sgi.com
David Borman dab@cray.com
Philip Budne phil@shiva.com
Randy Butler rbutler@ncsa.uiuc.edu
Lida Carrier lida@apple.com
Yee-Hsiang Chang yhc@concert.net
Richard Cherry rcherry@wc.novell.com
Jim DeMarco jdemarco@ftp.com
Peter DiCamillo cmsmaint@brownvm.brown.edu
Joseph Godsil jgodsil@ncsa.uiuc.edu
Olafur Gudmundsson ogud@cs.umd.edu
Peter Honeyman honey@citi.umich.edu
Holly Knight holly@apple.com
Vincent Lau vincent.lau@eng.sun.com
Tony Mason mason@transarc.com
Bill Melohn melohn@auspex.com
Paul Milazzo milazzo@bbn.com
Greg Minshall minshall@wc.novell.com
Robert Morgan morgan@jessica.stanford.edu
J. Bradford Parker brad@cayman.com
Eric Smith
Mike Spengler mks@msc.edu
Sven Tafvelin tafvelin@ce.chalmers.se
Kathleen Wilde wilde@decvax.dec.com
Preston Wilson preston@i88.isc.com
Nancy Yeager nyeager@ncsa.uiuc.edu
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