In every server room, I always keep a spreadsheet showing how many VA and W each UPS is rated for, and how many VA and W each system draws, and which UPS's each server is connected to. It's a pain because I don't blindly add up all the max power supply ratings (which are typically about 5x higher than the *actual* max power requirements of the box)... In order to get the measurement, I have to plug a power strip into a kill-a-watt, and then plug both of the redundant power supplies of the box into the power strip, then stress the system for a couple of minutes, and record the measurements. This effectively solves a few problems (a) under sizing UPS's, which I've seen bite other admins, whose data centers crash under load etc, and (b) over sizing UPS's, which is what most admins do, and wastes money and space, and creates unnecessary waste.
Anyway, all that is just a tangent. Here's what I really came to say: Yesterday, I turned on a new server, took my power measurements, and was blown away to find that the system drew a maximum of 110W and 120VA, including 10% margin for error. Dang! They're getting good at power reduction. Not long ago, I expected less powerful servers to draw 300-500 or so, *actual* measured peak. BTW, assuming a typical server with nothing but cpu, ram, and disks in it, the way I stress the system is to launch a zillion threads of "cat /dev/urandom > /dev/null" and gzip, until "top" shows me I'm CPU starved... I have found experimentally that stressing the disks and/or network and/or other IO makes no noticeable difference to power consumption. If there were any other power hungry components such as GPU, I would need to find a way to stress that component as well.
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