From owner-freebsd-current  Wed Sep 30 15:24:54 1998
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Date: Wed, 30 Sep 1998 23:20:33 +0100 (BST)
From: Andrew Gordon <arg@arg1.demon.co.uk>
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To: Karl Denninger <karl@Denninger.Net>
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Subject: Long SCSI probes (was Re: Long IDE probes?)
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On Wed, 30 Sep 1998, Karl Denninger wrote:
> 
> What I don't understand is the reason for the long probes (that is, more
> than a second or two) in any of the disk devices.
> 
> IDE by definition is probed by the BIOS before boot.  Either the disk is
> there or it is not, and you don't get out of POST and to Boot until that's
> determined.  Therefore, a long wait there is COMPLETELY pointless.
> 
> SCSI devices similarly are probed by the adapter BIOS.  Again, there is no
> reason for the long wait that I can fathom.

Note that the SCSI bus is reset before probing; SCSI devices vary wildly
in their reaction to this.  I have a tape drive that, if there is a tape
in the slot, engages in considerable tape movement (presumably to detect
the tape format/capacity) - this device requires (pre-CAM) SCSI_DELAY=23
to survive rebooting with a tape loaded.  Even disc drives vary from
near-instantaneous to several seconds response time.


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