QBUS SCSI card...

From: Brian Chase <vaxzilla_at_jarai.org>
Date: Tue Feb 25 01:14:00 2003

On Mon, 24 Feb 2003, Zane H. Healy wrote:

> > I'd say it's more the difference between the throughput of the DEQNA
> > and the throughput of the RQDX3/RD54 than it is between the difference
> > between MFM & modern SCSI. My fileserver will spew data a good bit
> > faster than the DEQNA can process it. The Qbus ethernet is the
> > bottleneck.
>
> I'm pretty sure you're right about the DEQNA being the bottleneck.
> Have you clocked the throughput on the DEQNA? I'm guessing it's about
> 1Mbyte/Sec max (in reality I'd guess it's FAR lower).

Given that it's 10Mb/s ethernet, seeing something like 1MB/s would
definitely be an upper limit. I do know that, at least with NetBSD/vax,
the port maintainer worked hard to get the DEQNA and DELQA (running in
DEQNA mode) to operate as efficiently as he could. It's been a while
since I got to play with my Qbus systems, so I don't recall the actual
throughput being seen. From a list mail of his:

-> On Fri, 10 May 2002, Anders Magnusson wrote:
->
-> > You can look at the original DEC driver that were in NetBSD, it
-> > have some of the compensation code for bad DEQNA's. Note that the
-> > DEC driver is quite slow; it could almost reach 200k/s (in both
-> > directions). The new one I wrote peeks about 500k/s.

I was seeing something close to 500KB/s on my systems, too.

> IIRC, the Q-Bus can only handle 3Mbyte/Sec. I think all the memory
> ops go over the ribbon cables (isn't the q-bus limited to powering the
> RAM, it's been a 2-3 years since I looked at a Q-Bus VAX and my memory
> stinks at times) so you should have a mostly free pipe between the
> DEQNA and the CPU.

Another thing to keep in mind, IIRC, is the position of the modules
along the Qbus chain.

> It would be interesting to have a Q-Bus FDDI adapter (DEFQA) and see
> how much more performance you could get using it, since it will
> saturate the Q-Bus. I think I'll have to look into seeing what it
> would take to set up such a test.

Ouch. I bet that'd be pretty painful for something like a MicroVAX-II
class machine; still, I'd love to see it done!

-brian.
Received on Tue Feb 25 2003 - 01:14:00 GMT