[Beowulf] DC Power Dist. Yields 20%

[Mark Hahn]

> 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?

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.