Forcasts, why won't anyone believe them?

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1

10 years ago, how many folks remember going to the phone company
and telling them "I need 600 phone lines in my basement." And the
phone company replying, "No one needs 600 phone lines, here is 6."
"No really, I need 600 lines in the next 12 months." The phone
company replies, "When you need them, then we'll install them."
"How long will it take." The phone company replies, "Don't worry,
we know what we're doing, that's none of your concern."

This was followed by the phone companies complaints that the Internet
wave hit them "without notice." Even though ISPs had been giving them
forcasts about the demand, the phone companies didn't want to make
the investment because those Internet companies might disappear in
3 months and leave a bunch of unused capacity.

Internet companies and web hosters have been giving power companies
forcasts for several years about their electrical demands. And once
again, the reply usually was, "No one needs 10 Megawatts for an office
building, here is 10 Kw." "No really, we need 10 Megawatts." The power
company replies "Don't worry, we know what we're doing."

If you look at the last three stage 3 alerts, there has always been
extra power available in the Western electrical grid. The problem has
been one of credit, not power.

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.

2

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

3

: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.

On a somewhat related note, it would be very useful to see manufacturers
include info on maximum transient loads (e.g., upon power-up, card
insertion, etc.) and practical constant draw on a per-chassis and per-card
basis. Such would be helpful in datacenter power plant design as well as
for offering data to the local 'edison'. Some manufacturers do so, though
it'd be nice to see it become common practice.

-brian

4

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