Are fileservers a waste of money

[Charles Hedrick]

I don't think anybody really has a complete answer to this question.
However I have at least some informed comments.  First, fileservers in
general may or may not be a waste of money, but *your* fileserver seems to
be.  You have a 3/260 with a XY451 controller.  Our results (which agree
with Sun's configuration guide, by the way) suggest that a 3/260 isn't all
that much faster than a 3/160 when used as a file server.  (It's a dandy
machine for real computing though.) Furthermore, it is being crippled by
the XY451.  You'd almost certainly get better throughput from one of the
3rd party fast SCSI disks on a 3/60 than from this file server, and at a
fraction of the cost.

Both Sun and other tests agree that the Sun shoebox is similar to network
access to an unloaded file server.  Sun originally (back when the 3/50
first came out) said that both were about 1/2 the speed of a "real" SMD
disk.  However SCSI technology has improved since those tests.  (Those
were the days of the XY451 and Eagles.)  It appears that with good
embedded SCSI disk controllers you can now get almost as good results out
of local SCSI disks as SMD (indeed some results suggest better, but they
tend to be comparing with less than optimal SMD controllers), at least in
single-user configurations.

In the worst case, it seems that swapping from a file server is
a disaster.  The worst case assumes
  - that all of your clients are swapping their hearts out at the
	same time
  - that you're comparing to local swapping disks using the best
	SCSI technology, and not the old Sun shoeboxes
  - that you have no more I/O bandwidth in your file server than
	on a client.
In that case, 6 clients are going to see less than 1/6 the swapping
performance they would see if they had local disks.

However, you may not have that worst case.  Here are things which
may combine to make a file server reasonable:

  - your clients may not all need to swap at the same time.  If they
	are using Lisp, this means you've put lots of memory in them.
	Note that this strategy has to be used on all your machines.
	If you have a couple of machines without enough memory, then
	they may swap continuously.  In that case they'll degrade
	even machines that have enough memory.  Enough memory means
	enough to keep the swap rate down, not to totally eliminate
	swapping.  Even the 12M machine will need to swap now and then,
	and when it does, it will get killed by the 4M machines.

  - you may be able to afford more I/O throughput on the server than
	on an individual client.  E.g. you may be able to use more
	disks in parallel, or more memory as a cache (both on the
	controller and in main memory).  You'd certainly do better
	with one of the new generation of SMD controllers,
	particularly if you're running a release of SunOS that doesn't
	do overlapped seek on the Xylogics controllers.

At the moment we are still using 3/50's and 3/60's in diskless
configurations.  However all of the proposals I've made so far for
Sparcstation 1's have involved local 100MB disks.