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From: jackw@hpdmd48.HP.COM (jack wood)
Newsgroups: comp.periphs
Subject: Re: Info Request - SCSI vs. ESDI
Message-ID: <15370004@hpdmd48.HP.COM>
Date: 11 Jul 90 20:59:44 GMT
References: <1990Jun29.184102.11637@cbnewsi.att.com>
Organization: Hewlett Packard - Boise, ID
Lines: 49


>I have a question about SCSI vs. ESDI.  A friend of mine just acquired
>a Data General AViiON 5000 Unix Server.  He has to decide whether to use
>ESDI, SCSI or both drives.  It will be the same drive for either controller so
>seek time, rotational latency, and head transfer rate don't matter.  They both
>also use the same VME bus.  

There is a big difference between the performance of multiple disk
configurations of SCSI and ESDI.  For a really good article on the subject, 
see MIPS Magazine (now called Personal Workstation), June 1989.  The machine
tested in that article was an 80386-based machine running SCO Xenix, but
I think that the results can be extrapolated to your configuration.  In the
article, benchmark data is presented showing that the ESDI disk and the 
SCSI disk being tested had about the same performance in a single disk
configuration.  However, as more disks and more processes were added to the
test, the SCSI disk system far outpaced the ESDI system.  

The reason for that is that the ESDI disk will hold the channel while it is
performing a seek, while the SCSI disk will disconnect, letting another
disk use the channel.  I think that your friend would be much better off 
using the SCSI interface.


>He has two drives and in the future may be getting a third.  His applications
>are written in COBOL and use some type of ISAM layout, so he expects to be
>doing lots of transfers of small records.  The applications are typical of a
>small business, payroll, billing, customer info, etc.
>

>Greg Romer    romer@csd5.nyu.edu or romer@spunky.cs.nyu.edu


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Jack Wood
Hewlett-Packard 
Boise, ID
208-323-4529
"The opinions expressed above may or may not be the opinions of my employer"