North American Network Operators Group

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RE: Forcasts, why won't anyone believe them?

  • From: Roeland Meyer
  • Date: Tue Jan 16 22:55:57 2001

The assumption is wrong. A server motherboard and CPU draws the same power
regardless of what it's doing. Lap-tops and the like are different and you
actually pay extra for that design. Most circuts these days are nmos
technology. Only in cmos does the power go up with the frequency. Peripheral
usage, like disk drives, are also constant since the largest power draw goes
to keeping them spinning. The seek mechnics are trivial. Floppy drives and
cd-rom drives are different. But, most servers do not keep those spinning
constantly. Ergo, for all intents and purposes, servers are a constant power
draw. They can be rated.

But, isn't this a topic for the DataCenter list?

> -----Original Message-----
> From: Jeff Cours [mailto:jeff@ultradns.com]
> Sent: Tuesday, January 16, 2001 4:18 PM
> To: nanog@merit.edu
> Subject: Re: Forcasts, why won't anyone believe them?
> 
> 
> 
> 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
>