Date: Thu, 4 Nov 1999 18:19:52 +0000 From: Mark Ovens <mark@ukug.uk.freebsd.org> To: Marc Wandschneider <MarcW@Lanfear.com> Cc: "'Colin Campbell'" <sgcccdc@citec.qld.gov.au>, questions@freebsd.org Subject: Re: SCSI v IDE Message-ID: <19991104181952.A318@marder-1> In-Reply-To: <13D5F9EDFD72D211BC3100105A1C2233054956@akira.lanfear.com> References: <13D5F9EDFD72D211BC3100105A1C2233054956@akira.lanfear.com>
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On Wed, Nov 03, 1999 at 05:31:15PM -0800, Marc Wandschneider wrote:
>
>
> > -----Original Message-----
> > From: Colin Campbell [mailto:sgcccdc@citec.qld.gov.au]
> > Subject: SCSI v IDE
> >
>
> > I have read in many places that SCSI is "better" (due to the
> > ability of
> > the controller to issue multiple commands to the disks). But
> > if I have two
> > IDEs, each on its own controller is there any real performance benefit
> > with SCSI, assuming the disks are similar in performance
> > characteristics?
>
>
> SCSI disks still tend to be faster on spin speeds and access
> times. up to 10k for SCSI vs like 7200 for IDES (and I still think that
> most of the latter are 5400)
>
> As far as I'm aware, the UDMA and all that jazz that IDE drives
> do still isn't as good as what SCSI does -- ie. you're still going to
> get better multitasking, especially on an Un*x operating system out of a
> SCSI disk.
>
The big advantage SCSI has over IDE is that the hardware is
intelligent and so works with much less CPU overhead than IDE. It
just gets on with the job of shifting data and leaves the CPU free
to do other things. That is one of the main reason SCSI is more
expensive than IDE.
One good real world ways to see the difference between IDE and SCSI
is copying large amounts of data from a CD-ROM to disk under Windows.
Even with NT (which is supposed to be multi-tasking) if you start
copying a large volume of data from IDE CD -> HD and watch the CPU
usage meter in Task Manager it will run way high with IDE and hardly
anything with SCSI.
On my machine (K6-233, 64MB) it was ~95% and that slowed everything
else down to a crawl, clicking in a partly hidden window would
result in several seconds wait as first nothing happened, then the
window outline was drawn, and finally the window contents. When I
changed to all-SCSI the CPU utilization dropped to ~5% and the
window raising happens almost immediately, practically as fast as
normal.
> of course, my knowledge might be way out of whack here ....
>
> marc.
>
>
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