Power Corrupts

Pleased to Meter

My plug-in electricity usage meter arrived from Maplin (N67FU). It cost just just a tenner and gives me the ability to see if my careful purchasing has actually delivered me an efficient server. You plug it into a mains outlet, and then the device to be measured connects to the three pin 13 amp socket in the front. It has a maximum power rating of just over 3Kw so it should be enough for an Intel i3 (laffs), and the flat-ish design means wall-warts shouldn't be a problem.

It works really well, and it's cheap as chips, but the niggle I've had with it is reading the LCD screen. Parts of the display are really tiny and my eyes aren't what they used to be. Plus mains power sockets tend to be in low, poorly lit places, making reading harder still. The only real issue has been the mode indicator, which is the smallest bit and block inverse. (Who dreamed that up?.. I can understand from a design point of view how you'd want to differentiate that a little, but they might as have well used Egyptian Hieroglyphs!)

Meter mode indicator shown top right.

Thankfully the screen layout changes enough so that you can work out which mode you're in, and it's mostly about that big number in the top left so I can get by without needing a flashlight and my reading glasses.

Measuring Up

The existing Pingu had to be shut down to install a replacement /home and /data drive. I use 2.5" laptop drives these days to keep check on the noise and heat, and this disk was the first one I'd bought after switching to the policy four years ago. Last week it started to fail big time, throwing numerous errors, making loose rattling noises and finally showing files with zero bytes size. I won't bore you with the gory details because I have regular backups, but it gave me the chance to plug in the power meter and see how much juice my trusty old server has been using all these years.

The Via system board is rated at 11 watts, there's an SSD, two laptop drives and a 2Tb desktop drive for my auto-backups, which is normally asleep. So after allowing for a power supply efficiency of 80%, I'd estimated about 25 watts in total, but found it actually used just under 27w. I'm pretty sure it's the disks that are dragging it up so high, but until I unplug them it's just an educated guess. But having the electricity meter means I can be a little more pragmatic about future disk purchases. Maybe one day SSD's will be big enough and cheap enough to fulfil my data storage requirements.

Next to be benchmarked was the new Intel i3 based machine. The bulk of the software, two database servers (Postgresql and mySQL), as well as Apache2 had already been installed but not configured. And as I blogged last time, Minecraft Server was ready to go. Turning on the machine it peaked for a few seconds at 20 watts and then dropped to a very reasonable 14.5 watts. It pretty much stayed at that value until I started the Minecraft service and then it went up by about ½ a watt. I measured CPU temperature by installing LM-Sensors and CPU utilisation was monitored using the Top utility.

With one player joining the game the power rose to about 15.5 watts and (by pressing 1 while running top) I was able to see that all four of the CPU cores had started to register light utilisation. (So I stand corrected, Minecraft Server does use multiple cores - thanks to Dr Vesuvius for that heads-up).

top - 18:47:19 up 1 day, 22:48,  1 user,  load average: 0.18, 0.12, 0.08
Tasks: 106 total,   2 running, 104 sleeping,   0 stopped,   0 zombie
%Cpu0  :  5.6 us,  0.7 sy,  0.0 ni, 93.4 id,  0.3 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu1  : 18.6 us,  1.0 sy,  0.0 ni, 80.4 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu2  :  3.3 us,  0.0 sy,  0.0 ni, 96.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu3  :  6.4 us,  0.3 sy,  0.0 ni, 93.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   8127440 total,  1199480 used,  6927960 free,    19984 buffers
KiB Swap:  3090420 total,        0 used,  3090420 free,   862192 cached

Some of this could be the other services running but without the Minecraft Server there's very little utilisation on the other cores.

With the case lid removed the CPU temperature drifted up to around 45 degrees centigrade and the fan still turned at it's original lazy rate. I gotta admit, that's better than I expected.