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. 1 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. 2 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 3