Measuring power

[Nick Cleaton]

On Wed, 2009-04-29 at 09:42 +0100, Andrew Beattie wrote:
> This is a long way off topic but I'm hoping that someone here might be 
> able to share a clue...
> 
> I need to measure the power used on dozens and dozens of servers.
> 
> I need a breakdown by server, not a total for the room.
> 
> (more specifically, I want to calculate the power cost per server per year).
> 
> Added difficulty:  I want to do this non-intrusively.
> 
> I can't go round, yanking out cables and inserting in-line meters.
> 
> So, I got a clamp meter.  But contrary to my expectation, that only 
> works if I can separate the individual wires in the power cable - not an 
> option.
> 
> So, I'm stuck.  Is there any non-intrusive way to measure the power 
> consumption of my servers?

No easy way, it seems.  If you *really* need to do this to the point of
entertaining loony schemes...

One possibility might be to measure the heat output of the servers,
rather than the electricity input.  If you assume that the servers lose
heat mainly by pumping hot air out with fans, you'd need to measure both
the air flow rate and the difference between output air temperature and
input air temperature.