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From: taylor@anthrax.Solbourne.COM (Dick Taylor)
Newsgroups: comp.periphs
Subject: Re: Info Request - SCSI vs. ESDI
Message-ID: <1990Jul12.183953.17332@Solbourne.COM>
Date: 12 Jul 90 18:39:53 GMT
References: <1990Jun29.184102.11637@cbnewsi.att.com> <15370004@hpdmd48.HP.COM>
Sender: news@Solbourne.COM
Organization: Solbourne Computer, Inc.
Lines: 46

In article <15370004@hpdmd48.HP.COM> jackw@hpdmd48.HP.COM (jack wood) writes:
>
>>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,
>...
>
>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.
>

Actually, seeks are overlapped on the Ciprico controller (a version of which
is used in the AViiON).  Experience gained on an AT-bus '386 is unlikely to
be valid when extended to cover VMEbus workstations.

ESDI is usually faster because the controller handles its cache better than
the drives do (with these controllers and disks, anyway).  SCSI also has 
higher per-command overhead (adding the drive overhead and the HBA overhead,
plus things like disconnect times).

As SCSI develops and as the new drives become available in workstations,
SCSI will end up having an edge in many applications.  This will happen
because SCSI should continue to hold a cost advantage and the limiting
disk performance is the same -- the speed of the drive.  SCSI is also
better-poised to head for drives beyond 24MHz and technologies like ZBR.

As far as a recommendation goes, I'd suggest that your friend try to get a
chance to benchmark his applications on a machine configured with both ESDI
and SCSI.  It's really the only way to know whether it makes a difference
for him.




NOTE:  The foregoing is based on personal experience with Ciprico and its
products, but does NOT represent the opinions of either Ciprico or Data
General.  If they want to say something, they will say it themselves.