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From: jqj@GVAX.CS.CORNELL.EDU (J Q Johnson)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Ethernet Suffering
Message-ID: <8705021103.AA16064@gvax.cs.cornell.edu>
Date: Sat, 2-May-87 07:03:35 EDT
Article-I.D.: gvax.8705021103.AA16064
Posted: Sat May  2 07:03:35 1987
Date-Received: Tue, 5-May-87 00:46:01 EDT
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Reply-To: jqj@gvax.cs.cornell.edu (J Q Johnson)
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Organization: Cornell Univ. CS Dept, Ithaca NY
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Charles Hedrick notes that 20 to 40 diskless SUNs is a resonable load on
an Ethernet.  Although our experience at Cornell is consistent with this
estimate, one should be a bit careful:  small software and usage changes
can make for big changes in behavior.  For example, on our main Ethernet
(about 25 diskless SUNs plus 75 other machines, total less than 25% load)
we observe that at least 1/2 of the SUN load is ND traffic.  ND is not
efficient in its use of Ethernet bandwidth, and I would expect the total 
load offered by the SUNs to drop, perhaps precipitously, when SunOS4.0
arrives.  Similarly, slightly better caching strategies in clients can
make a big difference, as can adding a bit more memory (we do wish our 
3/50s had 6MB!).

Perhaps most important, don't attempt to generalize from diskless SUNs
to PC-ATs (or even to diskless VAXstations).  The PCs won't be paging
across the network, don't run a multitasking OS, have typically smaller
program sizes than Suns and longer process lifetimes, etc.

All the above points to being able to support lots of diskless workstations
on your network.  On the other hand, it would be foolish to design a
network that didn't make provisions for saturation.  If you don't put
in bridges or gateways initially, at least locate your servers near
their clients so you can get the benefit of installing bridges later if
you need to.  Leave your PCs with a couple of empty slots so you can add
more memory (for a RAM disk or whatever) later if need be.  And so on.
Don't assume that any load analysis you do today will still be valid in
1989.