Forcasts, why won't anyone believe them?

Wed Jan 17 03:07:48 UTC 2001

Thi is largely card dependent I suspect.  Cisco specifies 100amps I
believe for their dc power supplies on 12008s, a company I worked for
previously ran 25 amp circuits with 20 amp breakers to each, and even the
burst of a sudden power on doesn't get near enough to that to cause a
problem.

	Brian

On Tue, 16 Jan 2001, Jeff Cours wrote:

> 
> 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
> 