I have a handy power meter which is useful for measuring the power consumed by my virtualization cluster under various loads.
Note in the figures below I’m only including the four cluster hosts. Not included: the NFS server (which is my development server, so I have it switched on all the time anyway), or the network switch.
With all four hosts idling, power usage of the total cluster was around 174-177 watts. To give you an idea of how much that costs to run, it would be about £263 p.a. at a typical UK rate for electricity.
Interestingly, with one host running, power usage was 50W (I would have expected it to be exactly one quarter), and with no hosts running, something consumes 7W. I suspect the PSUs leak a bit even when nominally off but with the hardware switch still in the ON position.
Under some moderately heavy loads (parallelized compiles in a loop) I was able to drive the power usage up to a maximum seen of 584W (£869 p.a.). Note that was a one-off, and most of the time it bumps wildly around the 300-500W range (unfortunately my simple power meter doesn’t do running averages).
So low power ARM this ain’t! One thing we can do to mitigate this (apart from turning it off) is to migrate VMs to a single node when load is low, and turn the other nodes off. That should save a fairly considerable amount of power.
I also installed lm_sensors so I could monitor temperatures and fan speeds, but there’s not really anything interesting to say. Under load the fans of course spin like mad (typically 3000 RPM), but the temperatures stay at a cool 40°C or so. Even though there is only one fan per motherboard (the CPU fan) there don’t appear to be any cooling issues.