North American Network Operators Group

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Re: rack power question

  • From: Michael Brown
  • Date: Tue Mar 25 18:14:21 2008

Alex Rubenstein wrote:
> As for how much, ask HP or IBM or whoever how many blades they can shove
> in 42U.
Coming from the "implementing the server gear" side of things...

If we're talking IBM gear (as that's what I know) the magic numbers are:
- 4 x Bladecenter H chassis in a 42U rack
- 14 x Blades per chassis
- 56 blades per rack

Each chassis has 4 x 2900W power supplies (plus two 1KW fans), so that's
13600W per chassis. 54400W per rack total power. (There's something to
think about - are you talking about providing 6KW of capacity, or 6KW of
a continual load to each rack?)

Naturally, that's redundant, so theoretical maximum usage per rack is
half that, 23200W. Plus, the blades available today don't draw enough to
fully load those power supplies. In the config I'm looking at now, a
single blade (2x Quad-core 2GHz Intel, 4GB memory, no hard drives) draws
232W max, 160W lightly loaded. Let's pull a number of 195W out of the
air to use.

The chassis itself draws 420W (assuming 4 I/O modules) plus a
hand-waving 400W for the fans, so a magic number of
(195*14+400+420=3550W) times 4 gives 14.2kW for a loaded rack. But you
need to make 54.4kW of power availble, which is relatively immense.
You'll find this requirement in most blade scenarios, so be prepared for
it. The plus side is that if you are the hardware provider in a co-lo
scenario and you own the chassis, you can meter and bill your customers
for the individual blade power (and a magic coefficient for cooling
cost) they use if you so decide.

So, as many others have already said, over 8kW in a rack is a
no-brainer. Getting those BTUs out of the rack into the datacenter is
easy to do (at least on the Bladecenter H). It's getting those BTUs out
of the datacenter that's usually a problem, except in your special
situation. Which I also am curious about.