Newsgroups: comp.arch
Path: utzoo!utgpu!watserv1!maytag!watdragon!watsol.waterloo.edu!tbray
From: tbray@watsol.waterloo.edu (Tim Bray)
Subject: Workstation Disk I/O
Message-ID: <1990Oct15.003424.271@watdragon.waterloo.edu>
Sender: daemon@watdragon.waterloo.edu (Owner of Many System Processes)
Organization: University of Waterloo
References: <14900016@hpdmd48.boi.hp.com> <2387@van-bc.wimsey.bc.ca> <143502@sun.Eng.Sun.COM> <6349@titcce.cc.titech.ac.jp>
Date: Mon, 15 Oct 90 00:34:24 GMT
Lines: 33

sritacco@hpdmd48.boi.hp.com (Steve Ritacco) wrote:
  Let's consider the SPARCstations, DECstations, Personal Iris, Mips Magnum,
  NeXT, HP s300/s400, Sony NEWS, etc.
  How do each of these systems handle their disk I/O, what are the cost/
  performance advantages of the approaches, what is the realized performance,
  what is the potential performance, and what is the bottle-neck?
 
Discussion followed, among which this from Vic Abell <abe@mace.cc.purdue.edu>: 
  It is very difficult to disable the effect of a good buffer cache when you
  really want to measure I/O device or channel speed.  So far I've not seen
  any test that does a good job of that, nor have I been able to construct
  one myself.

This is nearly right.  What you almost always want to measure is *unix
filesystem performance*, a complex aggregate of bottlenecks that is remarkably
independent in some respects of the performance of the underlying I/O hardware.

I have written (and posted to this group some months back) a benchmark named
'Bonnie' that claims to do at least some of what is wanted.  In particular, it
exercises sequential buffered/char and block I/O to large files, stressing
(separately) the file allocation and cache management code.  Finally, it does a
random I/O test that makes an *aggressive* effort to bust the caching mechanism
(IFF you can dedicate filespace many times the size of physical memory to the
benchmark).  I claim the numbers it produces are a useful metric to compare
certain aspects of filesystem performance from system to system.

The benchmark grows out of experience on the New Oxford English Dictionary
project at the University of Waterloo - a multi-year struggle against I/O and
memory bottlenecks.

I would be happy to provide the source code on request, and to collate results.

Cheers, Tim Bray (tbray@watsol.waterloo.edu)