One SCSI tape connected to 2 hosts?

From: Bob Lafleur <bob_lafleur_at_technologist.com>
Date: Fri Jun 21 09:48:43 2002

I guess I've abandoned the idea of hooking the tape drive to both
systems. It sort of worked, but I found when I had it connected this
way, when backing up under Windows, the drive would suddenly become
unavailable. Sometimes it would run for an hour, and then this would
happen. I don't know if the VMS system was sending it a reset, or what.
I didn't use it enough under VMS to know if Windows was interfering from
that side, but I did a few medium length tests and it seemed to be OK.

I'll just throw the DDS-2 drive into the MicroVAX (I might have to use
some sort of mickey-mouse mounting system if I can't find a mounting
bracket for a BA42B case) and find another drive for the PC.

   - Bob

-----Original Message-----
From: cctalk-admin_at_classiccmp.org [mailto:cctalk-admin_at_classiccmp.org]
On Behalf Of Huw Davies
Sent: Friday, June 21, 2002 10:12 AM
To: cctalk_at_classiccmp.org
Subject: Re: One SCSI tape connected to 2 hosts?


At 03:16 PM 16/06/2002 -0500, Doc wrote:
>On Sun, 16 Jun 2002, Bob Lafleur wrote:
>
> > I've noticed that my MV3100's SCSI host ID's are set to 6 - I
> > thought this odd, as host ID's are usually 7. Are all MV3100's set
> > to 6, or is mine unique? Anyway, I thought since my PC's host ID is
> > 7, I could connect my SCSI tape drive to both systems. So I ran a
> > cable from one connector on the back to my PC, and a cable from the
> > other connector to my MV3100. I figure it's a properly terminated
> > chain, as each host controller is terminated (I know the PC is, I
> > assume the MV3100 is).
> >
> > It *seems* to work OK. But can anyone tell me for sure if this is
> > "legal"? I'm sure I'm looking for trouble if I try to use the same
> > tape drive from both systems at the same time, but as long as I
> > don't do that, is this an okay setup? It would sure beat changing
> > cables every time I want to move the tape drive from one system to
> > the other.
>
>Bob,
> A few of the older SCSI "how-to" pages diagrammed just such a setup.

>I've never seen it done in real life, but it always looked like a
>reasonable idea to me, too.
> I just found out, talking to my boss, that both native Solaris and
>Veritas Volume manager support that type of configuration.
> It's also relevant that you can run IP-over-SCSI between hosts, and
>ISTR that the original Beowulf code provided just that for fast
>intra-cluster communication.

Of course Digital (and Compaq) supported systems with shared SCSI
storage
under OpenVMS alpha - not surprisingly they were known as SCSI clusters.

You still needed ethernet for SCS traffic but it certainly worked.

Huw Davies | e-mail: Huw.Davies_at_kerberos.davies.net.au
                      | "If God had wanted soccer played in the
                      | air, the sky would be painted green"
Received on Fri Jun 21 2002 - 09:48:43 BST