[Beowulf] The fan from hell

[David Mathog]

Today I distributed database fragments out from the main server
to the 20 compute nodes.  This required the server to run gunzip
pretty much continuously for a couple of hours. The net result of
which was that CPU1's temperature rose from 55C to 60-61C.
Normally the fan on CPU1 sits happily at 5033 RPM. However
today it started to slow down.  In fact it slowed down below
3000RPM, which triggered an automatic shutdown of the server.

After a bit of experimentation I've now determined that
this wasn't a coincidence. This CPU fan really does run
slower when the CPU gets hotter.  It takes a
few minutes before it starts to slow down, but slow down it
does.  Not exactly the desired response for a fan on a hot CPU!
This is on an Athlon MP 2000+ processor and the fan is Dynatron
model that AMD used with the boxed CPU.

Any of the system vendors (or anybody else) out there have a
preferred brand of 60mm fan that doesn't slow down at 60C?

Thanks,

David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech