[Beowulf] Efficient UPS Aids Google?s Extreme PUE

Greg Lindahl lindahl at pbm.com
Fri Apr 3 13:43:00 PDT 2009

On Fri, Apr 03, 2009 at 09:14:24AM -0700, David Mathog wrote:

> In the picture on the OP's link the external PS does not look any bigger
> than a standard unit, which leaves very little room in it for the UPS
> battery.

The picture shows 2 things sticking out. One is the PS, the one on the
other side is a battery. There are 2 long wires (red,black) that run
from the battery to the PS.

I can't guess how long a battery of that size would last, but probably
more than a couple of minutes.

I'd bet that the main motivation for separate batteries was not cost,
but the 5-8% PUE gain. Separate batteries must cost a lot more in
maintenance and are less reliable, although a small failure that
knocks out 1 node is preferable to a 1/N chance of failure of N nodes,
if N is large.

I'd also comment that the airflow is not clean front-to-back. The fans
sit on the CPUs and blow down. This inhibits the front-to-back flow a
bit. If you look in modern servers most of them have a fan blow
front-to-back air over a tall heatsink over the processor. This is
smoother flow, plus it allows redundant cpu fans. And as someone else
mentioned, the airflow over the disks looks to be minimal. Disks don't
need that much air, but many modern designs have much better disk
airflow than this.

-- greg

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