Re: SCSI disks

Matthias Urlichs (smurf@work.smurf.noris.de)
3 Jun 1997 07:19:36 +0200

In dist.linux.kernel, article <865284976.7387@noris.de>,
"Leonard N. Zubkoff" <lnz@dandelion.com> writes:
>
> I stand corrected. I had completely fogotten about this very important
> fact. I wonder if one could simulate this aspect of SCSI function with a
> sufficiently intelligent IDE controller (though at that point, there would
> be significantly less cost advantage to IDE).
>
No way. IDE doesn't allow multiple outstanding commands so you'd have to do
it all in software. With SCSI, the disk can start to move the head to the
next place while you're still transferring the data from the old command.

All this, of course, assumes that you have a new-enough SCSI disk which
supports command queuing, and a SCSI adapter that's fast enough to
streamline command processing. Somehow, I begin to suspect that a $100 NCR
SCSI adapter is a bit better in this regard than the big Adaptec boards;
did anybody test this recently?

> matter, all modern disks divide the disk platter radially into zones with
> different numbers of sectors per track, and I doubt that information is

It gets worse. Some disks do this for every platter (i.e. the hierarchy is
platter-track-sector instead of track-platter-sector) because the realign
from one surface to the next takes longer than seeking to the next track
(of which you know fairly well where it is, reltive to the current one).

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