One SCSI tape connected to 2 hosts?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Mon Jun 17 00:33:42 2002

I remember an article or newsgroup post about five years ago that discussed
this. I remember there was a fellow in Germany who was using SCSI ID=4 for
one system's host adapter while he used ID=7 on the other.

I've found that Windows hits my SCSI channels at about 1 Hz, however, so this
procedure is not likely to work if Windows is one of the players. I have a
three-channel controller and it clearly shows activity on each channel at
about that rate. The odd thing is that the CDROM doesn't see a hit, but the
tape drive, which the Win98 backup program doesn't even see, though the device
manager does, gets tagged each time the bus is fiddled with. This makes for a
lot of waiting when the tape drive is doing an eject or a retension operation,
for which it would disconnect if Windows drivers supported that sort of thing.

When I was at Martin, we used a couple of ADAPTEC AHA1540's to try to
communicate between two PC/AT's. It made for quite a bit of raw bandwidth,
but was difficult to wade through the protocol. That was before Windows, BTW,
and success was limited to "making it work" but never was pushed to the point
of actually doing useful work.

Dick

----- Original Message -----
From: "Clint Wolff (VAX collector)" <vaxman_at_earthlink.net>
To: <cctalk_at_classiccmp.org>
Sent: Sunday, June 16, 2002 3:27 PM
Subject: Re: One SCSI tape connected to 2 hosts?


>
> Hi Bob,
>
> I've tried to connect a tape drive between a Windows 95? machine
> and a FreeBSD machine with limited success. Windows issues a bus
> reset whenever it gets confused (translate a lot!) which will
> abort any transfer taking place from the MV3100. FreeBSD seemed
> to be better about not bothering with the bus except for reboots,
> but wasn't reliable WRT transfers.
>
> What you really need is a PC driver that accepts the fact it isn't
> the highest priority device, and leaves the bus reset line alone.
>
> Clint
>
> On Sun, 16 Jun 2002, 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.
> >
> > Doc
> >
> >
>
>
Received on Mon Jun 17 2002 - 00:33:42 BST