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From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Message-Id: <199605010947.LAA08814@labinfo.iet.unipi.it>
Subject: Re: lmbench IDE anomaly
To: terry@lambert.org (Terry Lambert)
Date: Wed, 1 May 1996 11:47:43 +0200 (MET DST)
Cc: msmith@atrad.adelaide.edu.au, koshy@india.hp.com, hackers@FreeBSD.ORG,
        current@FreeBSD.ORG
In-Reply-To: <199604302033.NAA07754@phaeton.artisoft.com> from "Terry Lambert" at Apr 30, 96 01:33:01 pm
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> > That's about right.  The SCSI disk gets the chance to sort the I/O to suit
> > itself, optimising its performance.  The IDE disk only gets to look at one
> > transaction at a time, so it's at the mercy of the disksorting code in
> > the operating system.  I don't know that FreeBSD's disksort stuff is 
> > terribly wonderful, but I'd happily stand corrected.
> 
> The disksort stuff is pessimal.  Contact mday@elbereth.org for details.

The original poster was doing a couple of lmdd from /dev/rwd0a, the raw
device. Does disksort get in the way in this case ?

BTW, running a number of dd on /dev/wd0a works *much* better, you get
almost n times the bandwidth at least with up to 5 instances, what I
tried.

	Luigi
====================================================================
Luigi Rizzo                     Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it       Universita' di Pisa
tel: +39-50-568533              via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522              http://www.iet.unipi.it/~luigi/
====================================================================