Robert Moskowitz wrote:
> Karl R. Balsmeier wrote:
>> Hi,
>>
>> Running a bunch of CentOS servers on 2U supermicro equipment,
>> usually with 8 drives on Adaptec SmartRAID V or LSI Megaraid.
>>
>> In designing a rack in a data center, the question arises as to how
>> to measure the amperage the server uses, prior to investing in power
>> drops that actually do that for you, even remotely, for about
>> $260.00-300USD per unit. This number is the important one these
>> days in determining rack/datacenter design.
>>
> I use the Radio Shack Amp meter. It has an inductance jaw that you
> put over ONE wire to the device. This means you need a place on the
> circuit that separates the hot and neutral wires. I have a special
> rig: Mail plug - separate wires - Female receptacle. Of course I
> have to unplug the device, put this rig in, test, then put things
> back.
>
That's one way to measure the current, then multiply by the input voltage to
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.
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.
HTH
Mark
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