[1940] in linux-scsi channel archive
Re: Why SCSI disks rather than IDE disks? Re: SCSI disks
daemon@ATHENA.MIT.EDU (Jeff Andre)
Mon Jun 2 15:59:53 1997
Date: Mon, 2 Jun 1997 13:39:50 -0600
From: andre@sweng.stortek.com (Jeff Andre)
To: welbon@bga.com, lnz@dandelion.com
Cc: linux-scsi@vger.rutgers.edu
> 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).
>
> I'd say that's very unlikely, as I doubt the IDE interface specification feeds
> back enough information about the rotational position of the platter. For
that
> matter, all modern disks divide the disk platter radially into zones with
> different numbers of sectors per track, and I doubt that information is
> available either. Without it, one cannot even determine whether sector N and
> sector M are on the same track. It's impossible to do optimal seek
> optimization without a pretty detailed model of the disk layout and
> capabilities.
I cannot speak for IDE, but I believe a SCSI Mode Page of 0x0C, Notch and
partition page, returns the different zones.
While you might not be able to tell whether sectors are on the same track,
performance would be improved by ordering I/O based on increasing/decreasing
sector number. A good SCSI will do this outboard; I don't believe IDE can
do those outboard since it only handles a single I/O at a time. The IDE
device driver could (maybe it does) order them.
Jeff
