> I think the fundamental difficulty here is that for any given VS3100
> system, the host adapter can only be on ID 6 or ID 7.

I've wondered about this, in other contexts.  What if you rewired the
cable so that one host's data pin 7 is another's (say) pin 2.  All data
(including CDBs and status bytes and such) would need swizzling, but
each host could think it's (say) ID 7.

Of course, the host adapters would still have to be able to do target
mode.

>   VAX #1  SCSI-A ID 6
>           SCSI-B ID 6-.
>                       | <-- shared SCSI bus.
>   VAX #2  SCSI-A ID 7-'
>           SCSI-B ID 7-.
>                       |
>   VAX #3  SCSI-A ID 6-'
>           SCSI-B ID 6-.
>                       |
>   VAX #4  SCSI-A ID 7-'
>           SCSI-B ID 7

> And then I guess given that you have an even number of systems, you
> could tie the two open ends together to create a ring.

Does each machine have to have the same ID on both its buses?  I'd be
inclined to do

  VAX #1  SCSI-A ID 7
          SCSI-B ID 6-.
                      |
  VAX #2  SCSI-A ID 7-'
          SCSI-B ID 6-.
                      |
  VAX #3  SCSI-A ID 7-'
          SCSI-B ID 6

Then you could close the loop even with an odd number of machines, not
to mention having all machines basically the same.

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