[Discuss] Server Room Power

[gaf at blu.org (Jerry Feldman)]

On 10/12/2011 07:46 AM, Jerry Feldman wrote:
> On 10/11/2011 01:56 PM, Matthew Kowalski wrote:
>> Does anyone have any experience with running server equipment (Dell 
>> Power
>> Edges, HP Proliant DL G7s&  HP c7000 Enclosures) at 208 VAC instead 
>> of 120
>> VAC?  Right now we're running 20 Amp circuits at 120 VAC but I've been
>> reading some on the web about better efficiency at 208V along with
>> additional power available.  The main issue we're having is getting 
>> enough
>> power to the racks to run the power dense equipment.
>>
>> Given one form of Ohm's as Power (Watts) = Current (Amps) x Voltage 
>> (Volts):
>>
>> The max power out of a single phase 20A 120VAC circuit is 2400 Watts.
>> The max power out of a single phase 20A 208VAC circuit is 4160 Watts.
>>
>> Since only 80% of the power should be utilized the max power would be
>> reduced to 1920 Watts and 3328 Watts respectively.
>>
>> Am I missing something?  We've got a network power unit that can output
>> various VAC voltages and up to 3 phases so this is really more of a
>> distribution to the rack question.  I'm thinking all I need is an
>> electrician to add additional circuits, am I right?
>>
> We are running 2 208VAC circuits. We have 7 old Intel Whitebox systems 
> + 1 ReadyNAS (2 power supplies), 1 HP DL380 G7 VMware ESX and a few 
> other things. Before that on 120V, I had to split the power between 
> two different circuits including running a power cord across the 
> ceiling. I am now using a Metered C-24V Dual Input CDU 
> http://www.servertech.com/products/metered-pdus/metered-pdu-c-24vd
>
> One issue with computers is that while they are running normally, 
> things should be ok, but on startup, you are spinning up all the 
> drives and the fans.
>
Just a few additional things that I didn't have time for earlier. 
Several of my systems have dual power supplies, such as the HP, 
ReadyNAS, one Whitebox. They are plugged into the two different sides of 
the CDU.
Another issue is the receptacles, some PDUs have C20 outlets: 
http://goo.gl/5D8HA, and some others have NEMA 5-20R 
(http://goo.gl/L3GpJ). I preferred the 5-20R because all of my systems 
can plug directly into it without me having to add additional cables.
The reason we went to this configuration is that out IT department got 
involved with the purchase of the HP VMware server, and they wanted us 
to come up to company standards. They did not recommend the 24 outlet 
CDU, but they recommended the 12 outlet unit with an additional failsafe 
transfer switch. I didn't like that setup. One advantage is that it 
would have placed out single power supply servers on a switch if one 
power outlet failed.

-- 
Jerry Feldman<gaf at blu.org>
Boston Linux and Unix
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