Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!columbia!rutgers!topaz.rutgers.edu!hedrick
From: hedrick@topaz.rutgers.edu (Charles Hedrick)
Newsgroups: comp.unix.wizards
Subject: Re: How many packets per second from a Sun-3 file server?
Message-ID: <13745@topaz.rutgers.edu>
Date: Wed, 5-Aug-87 21:45:38 EDT
Article-I.D.: topaz.13745
Posted: Wed Aug  5 21:45:38 1987
Date-Received: Sat, 8-Aug-87 07:02:11 EDT
References: <2820@phri.UUCP>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 44
To: roy@phri.UUCP


I haven't looked at packets per second from Sun file servers, but
I did do a bunch of experiments that are related.  These were
done using multiple 3/50's attacking file servers with scripts that
did I/O intensive activities.  (Nothing fancy: just shell scripts
that did copies, deletes, C compilations, etc.)  I came to the
following conclusions:
  - a 3/100 with one Eagle is limited by the disk subsystem, not
	by CPU or Ethernet.  When it is running at full speed, it
	is using about 2/3 of the CPU.  I don't recall the exact
	data rate we got, but I think it was about 47 transfers/sec,
	which is consistent with your results.
  - two Eagles with one controller gave only a few percent better
	results.  This is not surprising, as the controllers are
	currently operated in a mode that doesn't allow parallel
	operation of two disks.  (This is supposed to be fixed in
	4.0, though as I recall I heard that claim before of earlier
	releases.)
  - two Eagles with two controllers caused CPU to become the limiting
	factor.  We got about 1.5 of one disk, which is not
	surprising when you consider that one disk used 2/3 of the
	CPU.
  - we saw no difference between the original Eagle and 450
	controller and a super-Eagle with 451 controller.  However
	I find this very hard to believe, since our subjective
	impression based on multiuser performance is that the
	super-Eagle/451 combination is fairly quick.
  - we saw no improvement in going from a 3/100 with 4MB to a
	3/200 with 8MB, where one disk was in use.  Of course with
	two disks and two controllers, there would almost certainly
	be an improvement, since in that configuation a 3/100 runs
	out of CPU.
  - we saw no reason to believe that the Ethernet subsystem ever
	limited performance.

I found the most consistent measure of load was disk transfers/sec,
from iostat or vmstat.

By the way, we understand that some people are using 8MB machines as
file servers.  Does anyone have any evidence that adding memory helps
performance, for a machine used only as a file server?  When people
add memory, do they also retune the kernel so that it uses more
memory for block I/O buffers?  (If not, most of that extra memory
will be allocated for user processes, of which there are presumably
none.)