*BSD News Article 88394


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From: Jed Clear <clear@netaxs.com>
Newsgroups: comp.periphs.scsi,comp.unix.bsd.freebsd.misc
Subject: Re: Bizarre SCSI problem (3 disks work, 4 don't) (2940UW/Quantum Atlas II)
Date: Tue, 04 Feb 1997 21:17:47 -0500
Organization: Net Access - Philadelphia's Original ISP
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Alan Judge wrote:
> 
> ajudge@maths.tcd.ie (Alan Judge) writes:
> >The 4 disks are numbers 0..3.  When *any* three disks are connected to
> >the ribbon cable, everything works fine;  I can access and use the
> >disks.  When all four are connected, the SCSI system fails quite
> >quickly.
> 
> Some more testing would indicate that things work fine as long as Ultra
> SCSI is disabled.  Though this setting gives lower performance than 3
> disks at Ultra speed.  My guess is that something like cable length is
> on the borderline and simply plugging in the extra load is breaking
> things.  Anyone know for sure?

I seem to recall the SCSI spec has a minimum distance between devices.
Ultra SCSI is really pushing things so this could be a problem.  I
think the minimum might be 1 foot, but there seems to be some bit errors
on that particular memory.  You might check the Adaptec WWW site or
their tech support folks.

-Jed