Forcasts, why won't anyone believe them?

Wed Jan 17 00:18:19 UTC 2001

Sean Donelan wrote:
> One thing that would help.
> 
> Sun, Dell, Cisco, Compaq, Juniper, etc.  Can you please start listing
> the true power draw of your equipment, not just the fuse rating.  It
> would make forcasting a lot easier, if we knew ahead of time how much
> the equipment will really draw.

I'm not sure they can. Doesn't the actual power draw of a piece of
equipment depend on what it's doing? For example, a rack full of Pentium
III's that are acting as routers are mostly doing integer calculations,
running bus transceivers, and driving communications links. That same
rack full of Pentium III's acting as a render farm for your favorite
Hollywood movie will be doing floating point intensive calculations,
wide-spread memory access, spinning the disk drives, and, because of the
extra heat, working any variable-speed cooling fans harder. I'd expect a
measurably higher current draw in the second case.

It might be possible to come up with some sort of average power draw,
but Electrical Engineers really hate to give out numbers like that
because people base their designs on them instead of on the worst case
power draw, and then when something fries the EE winds up getting the
blame. That's why most engineering disciplines derate components and
allow a safety margin, which I suspect is where the fuse rating comes
from.

- Jeff

-- 
Jeff Cours
Senior Engineer
UltraDNS, Inc