LINUX HOME SERVER – power consumption measurements

With the set-up of my LINUX HOME SERVER I choose components in the hope to minimise the power consumption (at the obvious expense of performance) of the system. The cost of electricity isn’t going down and I wanted to try and avoid an enormous bill each year just for having the server idel for long periods of time. As well as choosing power saving components I disabled anything in the BIOS that wasn’t going to be used (e.g sound, serial and parallel devices) in an attempt to reduce power consumption still further.

First I made a sort of back of the envelope calculation at what the maximum power consumption should be;
31W CPU (published TDP of the chip)
25W Motherboard/chipset (can’t remember where I saw this! – oh yes here…http://www.silentpcreview.com/forums/viewtopic.php?p=285356)
4W System disk
2W RAM
16W 2x Storage disks
78W TOTAL POWER CONSUMPTION BY COMPONENTS
104W Allowing for PSU 75% efficiency

That’s my target but I don’t have to guess because I borrowed a plug-in energy monitor that tells me the power consumption of any appliance.
 

So what the verdict?   Actually when I booted the machine for the first time the power consumption spiked at 105W (blimey that’s uncanny!) for a second or so then subsided to a steady 60W when the machine is totally idle (just sitting at the login screen). I should note that the server used 4W when turned off.

I wanted to dig a bit deeper and estimate the contribution of individual components the overall idle power consumption. so I started to systematically remove all the components I could
1. Turned off – 4W
2. Maximum recorded – 105W 
3. At Idle – 60W
4. As 3 but with the two storage disk removed – 42W
5. As 4 but with the ICYDOCK cage unplugged – 42W
6. As 5 but with the PCI SATA card removed –  39.5W*
7. As 6 but with a Hauppauge Nova-T tuner card installed  – 44.5W*
8. As 3 but with a Hauppauge Nova-T tuner card installed  –  65.5W*
The only other things I could unplug would be the cooling fans and I didn’t fancy doing that. 

*The meter measures to the nearest Watt – but in some readings the value oscillated up and down by 1W.

Overall I guess I’m pretty happy with 60W at idle. I saw a review of Windows Home Server Machines where they measured power consumption and it’s pretty comparable (the range was 40 to 55W) if a little on the high side. This is acceptable considering my server is a much more capable machine that the average WHS offering. I guess the most striking results are;
— Just how much power Hard Drives consume…my estimate is that each drive uses 9W of power just sitting idle.
— Having a PCI card sitting in the machine that I’m not using (the Hauppauge card) is undoing alot of savings made elsewhere – the card uses about 5 or 6W of power and is just sitting there doing nothing at the moment.
— Although not all PCI cards are the same (obvious I guess) they all consume a few Watts – the PCI SATA card is estimated to use about 2.5W while the PCI DVB-T tuner card about 5/6W. It occurs to me that a PCI-express based card (which operate at lower voltages) should consume less power – it would be interesting to do a comparison using a Sil3114 PCI-e card (if such a thing exists) or a PCI-e based TV tuner.

Cost implications…
Well if it runs 24 hours a day at 60W (idle) then my bill will be increased by about £65.

I’ve based this on my simple calculation;
0.06Kw * 24 = 1.44 kWh (kiloWatt Hour) per day
1.44 * 365 = 525.60 Total kWh per year
£0.1236  * = £64.96 Total cost of running the computer

Next steps….
I guess I must see if I can make use of the mobile style power saving capabilities of the setup yet more by using power management to power down most if not all of the system if it sits idel for long periods of time. I guess the obvious place to start is with the hard disks since they use so much juice.

149 Comments

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