On Tue, Aug 01, 2006 at 08:03:58PM -0700, Mark Schoonover wrote:
> get watts. I think a better way is to determine the max current that the
> system will use. If you have a 500 watt PSU, assume 85% efficiency, then by
> using the input voltage you can calculate the max input power the server is
> going to draw. I'd design the datacenter to support the max power level the
> server will need, not just what it takes to run the thing. Start up will
> draw the most power, approaching the max power output of the PSU, then it'll
> lower some once all the drives are up and spinning.
Using this method, you will probably overbuild for power.
Power supplies in good servers are much higher-capacity than is necessary
for the typical application.
Regarding drive spin-up, i think a reasonable number for spin-up of a
15k drive is 30 watts (i couldn't quickly find a spec for spin-up power,
but ~10 watts idle is 'typical' for seagate 15k drives). Three of
those per server is 90 watts. During spin-up time, the CPU(s) will be
idle so will be drawing a lot less power than they would at full load,
so you have a bit of savings there.
Depending on your application, overprovisioning your power might not
be a bad thing - next year's servers will probably use more.
> It's somewhat an art, but you can get reasonably close to the entire power
> draw of your rack. In a pinch, I've added up all the UPSes and told the
> electrician 12000VA. They'll know what to do with that number.
This is good advice.
The "kill a watt" meters referenced in another post are a great
suggestion too.
danno
--
dan pritts - systems administrator - internet2
734/352-4953 office 734/834-7224 mobile
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