Vern Burke, SwiftWater Telecom
I’ve just been reading a piece about Microsoft removing fans from their data center servers and that having a negative effect on their PUE numbers. I’ve written on this blog before about the problems with PUE, now we have proof that it needs to be put out of it’s misery.
In a nutshell, PUE is the ratio of power consumed by the IT equipment of the data center, versus the entire power consumed by the data center. A PUE of 1.0 would indicate a data center where all the power is being consumed by the IT equipment. A PUE greater that 1.0 indicates a data center where a certain amount of power is being consumed by other than IT equipment, the biggest chunk of which is cooling.
The problem I’ve written about before with PUE is the failure to take into account the actual work being accomplished by the IT equipment in the data center. Throw in a pile of extra servers just simply turned on and idling, not doing anything useful, and you’ve just gamed your PUE into looking better.
The problem shown here is even more damning. Microsoft determined that data center energy consumption could be reduced by removing the individual cooling fans from its servers and increasing the size of the data center cooling system. Since the increase in power for the data center cooling systems is less than the power required for the individual server fans, the data center accomplishes the same amount of work for less total energy consumption, an efficiency win in anyone’s book.
The side effect of this is that, even though the total energy consumption for the data center is reduced, transferring the energy usage from the fans (part of the IT equipment number) to the cooling (part of the non-IT equipment number) makes the PUE for the data center look WORSE.
Gaming the metric simply made it inaccurate, which was bad enough. Any efficiency metric that shows a net gain in data center efficiency (same amount of work accomplished for less energy consumed) as a NEGATIVE is hopelessly broken. This also has the side effect of making a mockery of the EPA’s Energy Star for data centers, since that award is based directly on the data center’s PUE.
Misleading, inaccurate, and now totally wrong, this sucker needs to go where all the other bad ideas go to die.