[Beowulf] help! need thoughts/recommendations quickly

Robert G. Brown rgb at phy.duke.edu
Tue Mar 2 08:59:55 EST 2004


On Tue, 2 Mar 2004, Mike Eggleston wrote:

> I realize this question is not specific to beowulf clusters... however,
> at 9a I'm meeting with an upset user about a bunch of workstations
> using serial termainals. Things don't happen as quickly as he wants:
> setup, problem diagnosis, throughput, etc. What solutions can I present
> for these problems (I realize this is just a quick summary!). Also,
> the serial terminals are running at 9600 baud over sometimes 50 meters.
> One table I found shows 60 meters is 2400 baud and 30 meters is 4800
> baud. I think this is part of the problem.

It really shouldn't be, if the wiring is decent quality TP.  Back in the
old days, when our department was basically NOTHING but serial terminals
running over TP down to a Sun 110 with a serial port expansion, we had
lots of runs over 50 meters (probably some close to 100) without
difficulty at 9600 baud.  Keep the wires away from e.g. fluorescent
lights (BIG problem), major power cables, or other sources of low
frequency noise.  Running parallel to a noise source over a long
distance is where most crosstalk occurs -- try to cross wires at right
angles.  Conduit can help as it shields, as well, but our wires were
basically thrown up in a drop ceiling haphazardly by "trained
professionals" a.k.a. graduate students, faculty, and sometimes a
shop/maintenance guy.

> Possible solutions I have thought of:
> 
> - user stops complaining and deals with the situation

Always a popular one.  To accomplish it you had better be prepared to
use force.  Bring duct tape to the meeting...

> - put ethernet->serial converts at the terminals so the terminals are
>   on the network

Sounds expensive.  Of course, terminal servers themselves are typically
pretty expensive, although we used to use them in the old days when we
finally had more terminals than our server could manage even with
expansions.  And then workstations started getting cheaper and we
converted over to workstations and ethernet and never looked back.

How is it that you're still using terminals?  I didn't know that
terminals were still a viable option -- a cheap PC is less than what,
$500 these days, and by the time you compare the cost of the terminal
itself, the serial port terminal server, the serial wiring, and the
incredible loss of productivity associated with using what amounts to a
single, slow, tty interface they just don't sound cost effective.  Not
to mention maintenance, user complaints, and your time...

> - put small VIA type boards whose image is loaded through tftp and
>   the serial terminals actually run from the via boards
> - what else?

Give the terminals to somebody you don't like, replace them with cheap
diskless second hand PCs on ethernet running a stripped linux that
basically provides either the standard set of Alt-Fx tty's in
non-graphical mode or basic X and as many xterms as memory permits.
Problem solved.

In fact, depending on the applications being accessed and whether they
CAN run locally, problem solved even better by running them locally and
reducing demand on the network and servers.

   rgb

> 
> Mike
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-- 
Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu



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