Subject: Re: SCSI wiring
To: der Mouse <mouse@Rodents.Montreal.QC.CA>
From: Tracy Di Marco White <>
List: tech-kern
Date: 08/09/2005 14:07:58
In message <200508091826.OAA20014@Sparkle.Rodents.Montreal.QC.CA>, der Mouse writes:
>>> I was thinking about connecting two SCSI buses with the data wires
>>> switched around, so that one bus's D7 (and therefore ID 7) isn't the
>>> same as the other's.  [...]
>> It would be easier to just reprogram the SCSI controller to use a
>> different ID.  Most of them support it.
>> More importantly, the arbitration isn't going to work right if both
>> systems think they're at ID 7 and the other is at ID 6.  They will
>> both try to use the bus at the same time.
>Won't you have the same problems if you teach one of the SCSI chips to
>use (say) ID 6?  Won't they both think they are "the" host on the bus?
>How would these two situations differ that makes one work and the other
>Or am I just exposing my ignorance of SCSI?  Is there a canonical
>reference somewhere I can go read to Learn All About It?

I've done this before.  I had an SGI Indy something running IRIX &
a PC running NetBSD sharing a scsi bus.  The controllers were each
on separate IDs, and it all just worked.  There are other things to
be concerned about, only mounting things read write one place, for
example, but other than scsi bus resets when either system rebooted
(which wasn't a big deal) it just worked.  This was more than 8 years
ago, too, since it was at my previous job I did this.