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SubjectRe: SCSI disks
An ide controller basically just provides your ide disk with an interface
to your bus. your machine deals directly with the drive, so anytime your
machine needs to get anything off the disk it has to spend a lot of time
dealing with the drive. With scsi the scsi controller accepts requests
from the cpu ques them and deals with them in order. If you have multiple
drives many requests can be handled simultaniously with much less cpu
overhead than would be required with a an ide disk. For me the biggest
noticable difference in performance on my desktop machine is the
performance of swap on a scsi disk versus ide.

As far as the mechanisms being similar, if you takke your basic crap
ide/scsi disk, say a quantum fireball, the same mechanism is used for both
the ide and scsi version and both of them run at 4500 rm and barring
serious i/o demands their performance is pretty similar. Certain drive
mechanism are available only as scsi devices however so if you were to
look at a seagate baracuda II the disk itself is physically faster 7200
rpm versus 4500 and has a faster average seek 8.8 versus 10.5 ms the
physical characteristics of the disk can make a serious difference.

In my environment (news servers, nfs and ftp servers, mail services,
workstation replacements) scsi makes sense. by viture of the fact that ide
is getting just absurdly cheap the price differential is getting pretty
bigger 8 gb of ide disks is about us$ 800 versus about us$ 2000 for 2
4.2gb wide baracudas and a 2940uw controller. But if you need like 30gb of
disk in a machine scsi is really the only way to go.

On Mon, 2 Jun 1997, Lawrence Chim wrote:

> Well...IDE may beat SCSI if IDE support Disconnect/Reconnect at least.
>
> W. Reilly Cooley wrote:
> >
> > I hate to continue to beat this subject into the ground, but exactly what are
> > SCSI hard drives considered to the superior to IDE? According to the fellow
> > who wrote "Upgrading and Repairing PCs" (who, as a PC technician, I don't
> > wholly trust), SCSI hard disks a mostly IDE disks with an additional SCSI
> > interface, (ie, the head-disk-assembly is the same, and most of the control
> > electronics.) Does SCSI provide additional commands which permit finer
> > tuning and/or error prevention/correction than IDE?
> >
> > It seems to be generally considered that SCSI is superior to IDE, but from
> > this guy's writing (excepting for multiple devices on the SCSI bus or really
> > fast HDs) SCSI provides no benefit. Pls. someone cursorily clarify.
> >
> > Wil
> > -------------------------------------------------------------
> > W. Reilly Cooley
> > NakedApe Consulting & Navi.Net representative
> > 1509 NE 10th Ave., #104 Portland, OR 97232
> > 503 287-2165 wcooley@navi.net
> > www.navi.net/~wcooley www.navi.net/~nakedape
> >
> > As a service, I provide analysis for viruses and poor grammar to senders
> > of unsolicited commercial e-mail at a rate of US$250 per hour. Delivery of
> > said correspondence constitutes a request for the aforementioned services
> > at said price.
>

__________________________________________________________________________
Joel Jaeggli joelja@darkwing.uoregon.edu
Academic User Services consult@oregon.uoregon.edu
ANTC & NSRC joelja@ns.uoregon.edu
--------------------------------------------------------------------------
"On two occasions I have been asked [by members of Parliament!], `Pray,
Mr. Babbage, if you put into the machine wrong figures, will the right
answers come out?' I am not able rightly to apprehend the kind of
confusion of ideas that could provoke such a question."
-- Charles Babbage


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