Power Limit Clarification

[Stephanie Labasan]

According to the SCC contest rules for this year, each team's cluster must be powered through "two 120-volt, 20-amp circuits, (each with a soft limit of 13 amps) for a total of 26 amps." This suggests that exceeding the 13 amp limit on either one of the PDUs would constitute exceeding the power limit. However, depending on how the power is distributed within a cluster hardware configuration, it is possible to exceed the 13 amp limit on one PDU, but still be below the limit on the other PDU. In other words, it may not be possible to evenly distribute the power across two PDUs. 

Our main question: is it legal to exceed the soft limit of 13 amps on PDU if the total power consumption across two PDUs is still below 26 amps?

Thanks!

Sincerely, 

Stephanie Labasan

University of the Pacific

[Andy Howard]

Hi Stephanie,

I'm not sure when an official response will come for this, so I'll answer based on previous participation in the challenge.

In the past years, the rules have been that if you exceed on either 13A PDU, it's exceeding your power limit. Yes, this does place constraints on balancing your power across two separate circuits. 

-Andy

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Andrew Howard

HPC Systems Engineer

Purdue University

[Molnar, Peter]

Thanks, Howard, for clarifying this. The rules have not changed for this year. 

Péter Molnár

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[Doug Smith]

To clarify the rules for power limitation.

You may not exceed 13 Amps on either circuit.

Yes, you may run into a circumstance where you can not fully utilize the
capacity on both circuits. In past competitions teams have had
configurations where their head node and Infiniband switch were on one
circuit while their compute nodes were on the second circuit. The
compute nodes while running at maximum potential ran at 12.75 Amps which
is fine but since their head node contained their storage it consumed
more power. Head node and Infiniband switch consumed 11.5 amps. There
was not enough room in the power budget for them to run another node in
just 1.5Amps.

In total they are wasting 1.75 Amps but they are in accordance with the
rules which state that you can not exceed 13 Amps on either circuit
regardless. This becomes and efficiency problem and a very valuable
part of the competition. Exceeding the 13 Amp limitation comes with
penalties and possibly disqualification.

NOTE: The APC 7801 PDU that you will be using has a two digit LED read
out of the current Amp level, it also has a little red LED which is an
alarm. We set the alarms at 13Amps which means if the alarm LED
illuminates you know your over the limit.

Doug Smith
Co-Chair SCC12

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