Thermal Problems

Mitchel Kagawa mitchel at
Wed Jul 23 15:04:38 EDT 2003

I run a small 64 node cluster each with dual AMD MP2200's in a 1U chassis.
I am having problems with some of the nodes overheating and shutting down.
We are using Dynatron 1U CPU fans which are supposed to spin at 5400 rpm but
I notice that a lot (25%) of the fans tend to freeze up or blow the bearings
and spin at only 1000 RPM, which causes the cpu to overheat.  After careful
inspection I noticed that the heatsink and fan sit very close to the lid of
the case.  I was wondering how much clearance is needed between the lid and
the fan that blown down onto the short copper heatsink?  When I put the lid
on the case it is almost as if the fan is working in a vaccum because it
actually speeds up an aditional 600-700 rpm to over 6000 rpm... like there
is no air resistance.  Could this be why the fans are crapping out?  I was
thinking that a 60x60x10mm cpu fan that has air intakes on the side of the
fan might work better but I have not seen any... have you?

Also the vendor suggested that we sepetate the 1U cases because he belives
that there is heat transfer between the nodeswhen they are stacked right on
top of eachother.  I thought that if one node is running at 50c and another
node is running at 50c it wont generate a combined heatload of more than 50c

Mitchel Kagawa
Systems Admin.

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