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From: wayne@ames.arpa
Newsgroups: comp.unix.wizards
Subject: Open question on NFS, efficiency, etc.
Message-ID: <8730@brl-adm.ARPA>
Date: Mon, 10-Aug-87 14:40:34 EDT
Article-I.D.: brl-adm.8730
Posted: Mon Aug 10 14:40:34 1987
Date-Received: Tue, 11-Aug-87 05:00:31 EDT
Sender: news@brl-adm.ARPA
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While waiting at my diskless Sun workstation for a "cp" to complete,
an obvious question wandered into my otherwise empty head.  When I do
"cp a b" on my workstation under NFS, what is in fact happening is
that disk blocks are being read on the server, forwarded over the
Ethernet to my workstation, processed briefly, sent back across the
Ethernet to the server, and finally written back to the same disk they
started from; a rather tortuous path at best.  So I did a quick set of
timings on a 2.3 megabyte file: the local "cp" gave 0.0u, 4.0s, 1:26
elapsed.  To get timings for running the "cp" directly on the server
(via "rsh") I timed both locally ("time rsh server cp a b") and
remotely ("rsh server time cp a b"); local was 0.0u, 0.3s, 0:21
elapsed and remote was 0.0u, 2.1s, 0:15 elapsed.  I don't know how to
time the server's part of a local "cp", but looking at "perfmeter"
didn't show any significant difference in CPU usage.  So in other
words, the time perceived by the workstation user went from 86 seconds
down to 21 seconds, with no apparent increase in server load!  Given
this, has anybody taken the obvious step of automating this process,
sort of like having "cp" say "hmm, both these files are on the same
server and the file is big enough to cover startup time; I'll just
have him do the copy for me"?  (I realize that "rcp" already does 
something like this for "remote-to-remote" situations, but then NFS is
supposed to make things more transparent, right?  And by the way,
"time rcp server:a server:b" gave 0.1u, 0.8s, 0:36 elapsed; not as
good as "rsh cp" but still a lot better than "cp"!)

Anyway, I realize this is the tip of a rather large iceberg (the "when
do you move the data to the computation and when do you move the
computation to the data?" question), and I have in fact been chipping
away at that iceberg myself (for example, I already have procedures
set up to do lengthy "find"s on the server itself).  But I was just
curious if anybody has done anything "scientific" about this rather
limited version of the general question?  Or UNscientific, for that
matter (like my proposed hacking of "cp" above).  Sure seems like
something obvious to look at for (e.g.) SunOS.

Well, my "cp" is finally done, so back to work ...

      Wayne Hathaway                  ultra!wayne@Ames.ARPA
      Ultra Network Technologies
      2140 Bering drive               with a domain server:
      San Jose, CA 95131                 wayne@Ultra.COM
      408-922-0100