high physical density cluster design -structural...

Jim Lux James.P.Lux at jpl.nasa.gov
Tue Mar 6 12:39:15 PST 2001

I fully agree with David's comments about thermal issues probably being the
big problem here.  The structural issue really isn't a big problem. Almost
any material can work for actually holding the boards (wood, plastic,
copper, steel, fiberglass, titanium, depleted uranium, etc.).  Likewise,
you're probably going to be stuck with N/2 power supplies, at best.

Getting the heat out, reliably, is going to be the BIG problem with any
homebrew tight packaging.  Commercial manufacturers do actually spend a fair
amount of money doing testing and going through lots of revisions (or they
copy a proven design from someone else...) to keep temperatures reasonable
with very limited air flow (lower flow fans are quieter and cheaper, so
there is an economic incentive for low flow).

I have had very bad luck with operating consumer gear in even mildly
elevated room temperatures (say, 35-40C).  For a grin, check out the
specified operating temperatures on a laptop (typ, 30C max), and then
compare that to the temperature in, for instance, a car sitting in the sun
(40-50C): clearly, they only expect laptops to be used on a desk in an
office).  Consumer gear has very small design margin.  They realize that
most people will be operating it in a reasonably air conditioned office or
house, and that if it gets too hot to sit in the room, they'll turn the PC
off.  And, if they get a few failures.. oh well, you're used to rebooting
from BSOD anyway. Remember, this is an industry that is positively PROUD of
getting their DOA rates down below 3-5%.  Hmm.. 64 computers, 5% DOA means 3
dead computers, out of the box....

I have been working out designs for a compact transportable cluster for
field use, and getting the heat out is the single problem causing the most
trouble.  in this context, I am only looking at 6-8 mobos in a package.
Vibe, shock, and power all have fairly straightforward solutions.  Heat does
not, especially if the air temp you are working in is 40C and 85% RH

-----Original Message-----
From: David Grant <davidgrant at mediaone.net>
To: Velocet <mathboy at velocet.ca>; Jim Lux <James.P.Lux at jpl.nasa.gov>;
rutile at fixy.org <rutile at fixy.org>; bcrl at kvack.org <bcrl at kvack.org>
Cc: beowulf at beowulf.org <beowulf at beowulf.org>
Date: Tuesday, March 06, 2001 12:18 PM
Subject: Re: high physical density cluster design -structural...

>This has been an interesting thread, but I do have a concern about
>appropriate cooling  with "homegrown" 1U chassis.  Yes, you can build a box
>the will physically support the hardware in a 1U form factor.  My concern
>would be long term, and not so long term heat related failures on CPU's
>and/or disk drives.....
>just my .02

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