From owner-freebsd-scsi  Sun Mar 29 23:07:15 1998
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Date: Sun, 29 Mar 1998 22:40:52 -0800 (PST)
From: Tom <tom@sdf.com>
To: Marc Fournier <marc.fournier@acadiau.ca>
cc: freebsd-scsi@FreeBSD.ORG
Subject: Re: Adaptec 2940UW causing system hangs...
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On Mon, 30 Mar 1998, Marc Fournier wrote:

> 	I'm slowly going through some of the more recent discussions in
> the archives about the 2940 controllers, and there seems to be alot of
> 'theories' bouncing around about reducing the transfer rate from 20Mps to
> 10Mps, in order to eliminate the problem.
> 
> 	2 questions ...
> 
> 	1. doesn't that defeat the point of UW?

  Yes.

> 	2. *where* is the problem? our drivers or the controller
> 	   themselves?

  Driver + drives.  The driver isn't as robust as it could be.  If it sees
funny stuff on the SCSI bus, it acts similarily :(

  Picking high-quality UW drives helps a _lot_.  Seagate Barracuda 4XL/4LP
work wonders.  The Seagate Hawks are supposed to be good too.

  I'm now Quantum-free after our last Quantum died!  Still no failures
with the Barracuda 4LP or 4XL drives.

> 	I'm going to downgrade mine to 10Mps tomorrow when someone gets to
> the office, but it seems me that this would defeat the purpose of *using*
> UW if its too much to handle :(

  Slowing the bus can prevent bus problems that are freaking out the
controller.

  You also might as well check the cable.  For real UW applications,
don't use that cheap plastic coated ribben cable you get for $5.

Tom


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