For some reason I've not seen the emails reference below directly from
the list; this is from Allison's followup, so I hope I've got the
attributions correct...
> On Thu, 02 Jun 2011 08:20:11 +0100 Pete Turnbull
> <pete at dunnington.plus.com> wrote:
> > Although some manuals do mention that you
should only use one hard
> drive
> > in a BA23 (eg the Maintenance Manual) I've seen several systems --
> > including mine -- do so with no problem. I've never seen a problem
> with
> > Write Gate, nor would I expect to. Like all other ST412-type
> > interfaces, the M9058 distribution card has the same write gate signal
> > wired to all the 34-pin HDD connectors in parallel. In fact the /only/
> > control signals not wired strictly in parallel on those connectors are
> > some of the drive selects.
>
> The M9058 is the RQDXE. Don't anyone ever read what I write, or am I
> really that bad at expressing myself? I wrote "the BA23 backplane
> distribution panel". That is *not* the RQDXE.
I do know, the BA23 backplane panel is not an RQDXE :-) I also know
that, no, M9058 is NOT an RQDXE. RQDXE is M7513 (and the smaller and
even more primitive RQDXE-1 is M9512).
M9058 is the distribution board from the BA123, and I referenced it to
point out that the drive control signals are all bussed to all the
drives, ie all the HDD ports, on a BA123 -- which is a device that does
officially and always has supported multiple HDDs. Proving any problem
is not to do with signals going to several drives at the same time.
I did read what you wrote -- I understood you to be saying that the
problem might be a result of Write Gate going to both drives and I was
pointing out that that wouldn't matter. At least, not unless both
drives are selected at the same time, which will only happen if the
drive select jumpers are misconfigured to select both at the same time,
in which case lots of things will go wrong.
> Yes, the power supply is a separate issue. And
yes, there is no issue
> putting two drives in the same BA23 if you use a RQDXE. However, if
> you plug in two drives using the built-in backplane distribution
> panel, you will have a disk crash, which I unfortunately have first
> hand experience of having to clean up after.
Well, then, two of my machines must be continually crashing silently and
miraculously recovering for the last two decades :-) Sorry, but I have
physical proof that two drives in a BA23 with no extras (like RQDXE or
other interface extensions) can work perfectly well.
--
Pete Peter Turnbull
Network Manager
University of York