[Beowulf] DC Power Dist. Yields 20%

Robert G. Brown rgb at phy.duke.edu
Sat Aug 12 06:56:55 PDT 2006

On Fri, 11 Aug 2006, Mark Hahn wrote:

>> http://www.eweek.com/article2/0,1759,2000867,00.asp
>> 20% is a lot, both in terms of consumption and cooling capacity. I'm
> the article says "up to 15%" at the facility level - did you get 20%
> by figuring a savings at the rack level, too?

FWIW, Rackable has been selling this for years now.  Their systems use a
beefy DC power system with rails and custom chassis that both runs
cooler up front and isolates the heat of power conversion from the
motherboards.  It actually looks quite lovely on paper and I have little
doubt that it works decently in practice -- for a price.  I don't
believe that the amortized savings in power consumption equals the price
premium, though... the usual problem with this sort of thing.  Great
idea, limited market, break even or lose a bit on the markup/margin.


> afaikt, the article is based on an assumption that everything is powered by 
> an online UPS, and probably that node PSU's are low-performance (say,
> 65%).  sometimes studies like this ignore fact that incoming power is 
> inherently AC (that is, only start looking at efficiency given DC supply.)
> I'd love to see DC gain more traction - PSU's are certainly one of the 
> flakier components in our systems, though per node (HP DL145G2), they only 
> contain 2 of 14 fans (or of 18 moving parts).  I don't know whether
> there's a reason to think many small AC-DC PSU's would be less efficient than 
> a couple really big ones (factoring in the cost and inefficiency of DC power 
> distribution).
> I'd certainly be interested in a distribution system (whether AC or DC)
> that avoided so damn many plugs and sockets and breakers and PDUs.
> I guess I'm more enthused about servers becoming lower-powered, and also 
> quite interested in better ways to dissipate the heat than raised floors and 
> traditional chillers...
>> curious how long it would take before DC supplied racks become cost
>> effective.
> well, there's already a standard DC supply - to the motherboard.
> one impediment might be that it's got +12, -12, 5, 3.3 and probably
> a couple others.  if it were just a matter of providing lightly
> regulated 12V, life would probably be a lot simpler.  and I'm not sure MB's 
> would be much more complicated, either, since the current
> main consumer, the CPU, already has a fairly flexible and high-power
> onboard dc-dc converter.  (I wonder how efficient it is, typically...)
> regards, mark hahn.
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Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu

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