Well, for starters, multiple hosts on a SCSI is a feature that the LINUX
drivers didn't support back in '95 or so when I exhausted my own interest in
such things. Secondly, the SCSI doesn't attempt to effect commands that are
only found on SCSI-II devices in the context of SCSI-I targets, but rather
"just gives up" and complains when it encounters a SCSI-I perfectly capable of
doing what the SCSI-II command wants, though with a couple of commands. Some
drivers for some systems do this, but not the ones in Windows, and not the
ones in LINUX that I saw. Their behavior, in fact, when confronted with some
devices, e.g NODEMs, or tape libraries, or, for that matter, SCSI bus
expanders was quite primitive. From what I recall, they didn't support
command queueing, didn't support disconnect, didn't support chaining, and
wouldn't do a number of operations without being "babysat" by the host.
The drivers did, apparently, work very well for handling disk drives. I don't
know how well they handled CD writers, as that was another issue of the time.
I've only seen a couple of SCSI printers, but they didn't deal at all well
with non-mass-storage devices. One local company developed a CDR/label
printer combo that completely fell apart under the LINUX SCSI. Of course, it
didn't fare well under Windows, either.
Perhaps that's changed, but I would be surprised.
The main annoyance was that if the software attempted to use a SCSI-II
command, and the device was a SCSI-I device, it just went "tilt" and didn't
attempt to recover by using the necessary two commands. Further, when it was
formatting a tape, which took some time, it couldn't do much else on the SCSI.
Dick
----- Original Message -----
From: "Pat Finnegan" <pat_at_purdueriots.com>
To: <cctalk_at_classiccmp.org>
Sent: Wednesday, June 19, 2002 10:01 AM
Subject: Re: One SCSI tape connected to 2 hosts?
> On Wed, 19 Jun 2002, Richard Erlacher wrote:
>
> > It's true, Windows is not a candidate for this sort of experiment, since
it
> > goes out willy-nilly tagging the resources it thinks it has every second
or
> > so. You'd think LINUX would have a fairly decent SCSI channel interface,
but
> > it seems to be even more limited than the ones in Windows.
>
> OK, what exactly makes you say this? I don't have a lot of experience
> myself in dealing with low-level SCSI other than connecting devices and
> using user-mode software to talk to them, so I don't know. However, I do
> know that there are IP over SCSI and probably other things for Linux that
> support, if not demand, multiple adaptors/systems being attached to the
> SCSI chain. With Linux's 'generic' scsi driver, you should be able to do
> just about anything with the adaptor that 1) the driver/hardware supports
> and 2) you can think of writing an application for.
>
> -- Pat
>
>
Received on Wed Jun 19 2002 - 18:46:37 BST