data center loading (was:Re: rack power question)

Wed Mar 26 14:15:18 UTC 2008

On Monday 24 March 2008, Deepak Jain wrote:
> While I enjoy hand waving as much as the next guy... reading over this
> thread, there are several definitions of sq ft (ft^2) here and folks are
> interchanging their uses whether aware of it or not.
[snip]
> A 30KW cabinet while one sounds lovely, a huge amount of space is going
> to turned over to most or all of a dedicated PCU and 1/15th of the
> infrastructure of 500KVA UPS (@0.9PF) including batteries, transformers,
> etc.
[snip]
> Even ignoring heat rejection, the battery + UPS gear for 500KVA (even
> with minimal battery times) is approximately the same size (physically)
> as the 12 cabinets or so it takes to reach that capacity.  [same applies
> for flywheel/kinetic systems]

This is certainly a fascinating thread.

One thing I haven't seen discussed, though, is the other big issue with 
high-density equipment, and that is weight.

Those raised floors have a weight limit.  In our case, our floors, built out 
in the early 90's, have a 1500 lb per square inch point load rating, and 
7,000 pound per pedestal max weight.  The static load rating of 300 pounds 
per square foot on top of the point load rating doesn't sound too great, but 
it's ok; we just have to be careful.  Our floors are concrete-in-steel, on 24 
inch pedestals, with stringers.

In contrast, a 42U rack loaded with 75 pound 1U servers is going to weigh 
upwards of  3,150 pounds (if you figure 300 pounds for the rack and the PDU's 
in the rack, make that 3,450 pounds).  When we get to heavier than 75 pound 
1U servers things are going to get dicey.  Also in contrast, a fully loaded 
EMC CX700 is about 2,000 pounds.

It sounds more and more like simply charging for rack-occupied square footage 
is an unsustainable business model.  The four actual billables are power, 
cooling (could be considered power), bandwidth, and weight.  When we see 
systems as dense as a Cray 2, but with modern IC's, we'll be treated to 
flourinert waterfalls again. :-)
-- 
Lamar Owen
Chief Information Officer
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772
(828)862-5554
www.pari.edu