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