Green Server

Last week I bought a consumption measurement device for 20 bucks. I wanted to know how much current is needed for various electronic devices I use at home, some of them on a 24/7 basis. I have got a home server running Linux, that I use as a NAS, print server, slim server (for streaming mp3 files to an mp3 device) and for experimenting a bit with Xen and Ubuntu. I have got also some other devices like a wireless access point (WRT54GL running Tomato), a cable modem, an external backup hard disk, a b&W laser printer and a few other electronic devices.

Of course, one of the most energy hungry device I have is the server, which is always switched on. I was expecting a consumption of about 60 W, because I tried to choose efficient components, some of which were listed on a review regarding a green computer consuming 54 W when idle. My hardware configuration is the following:

• Processor AMD 64 x2 EE 3800+, dual core and energy efficient version (which is actually quite cheap)
• Micro-ATX Mainboard M2NPV-VM with AM2 socket
• 2 GB of RAM (DDR2 PC4300)
• 2 Seagate 7200.8 250 GB hard disks used as a software RAID-1 array
• Power supply ElanVital 500W, ATX, with 80% efficiency.
• Plextor Plexwriter DVD burner

So I shut downed my server, plugged it in the measurement device and booted it. The value I could read on the device, after the reboot was finished and the server was idle, was higher than expected: 85 W. I was not very happy with that value and began to try to optimize it.

• I first tried to remove the DVD burner, but I got just 2 W of reduction, which was not good enough.
• Then yesterday I tried to install the last stable release of Ubuntu, which is Ubuntu 7.10 gutsy 32 bits version (I add previously Ubuntu feisty with a XEN enabled kernel). I was pleased to see that the server was only consuming about 68 W (DVD burner included). I then tried to re-install XEN and after rebooting saw that I was again at 85 W. So the XEN kernel had different options enabled that were not optimized for a good power management.
• I got back to the stock kernel and tried to activate the automatic spin-down of the hard disks. I did this using the command
• hdparm -S 60 /dev/sda
  hdparm -S 60 /dev/sdb
• which spins down the two disks after being idle for 5 minutes. I was able to grab a few watts and get down to 60 W, which is not too bad. I added the two commands in /etc/rc.local so that it gets executed automatically on boot.
• I then tried to activate the automatic CPU frequency scaling, so that when the processor has a low usage, its frequency gets automatically reduced, hence saving some energy as well. I was getting some problems using the module powernow-k8, so I updated the bios to the latest version (1201), which resolved that issue. I could then install correctly the cpu scaling daemon. I just had to run
• apt-get install cpufreqd
• and then edit the file /etc/default/cpufreqd and insert “powernow-k8” in the option CPUFREQ_CPU_MODULE (you can check which module you need to use here). With these two operations, the BIOS upgrade and the cpu frequency scaling, I was able to grab a few watts, getting down, when the server is idle, to about 53 W, which is already a lot better than the 85 W I was getting without tuning.

The options I might consider now are the following:

• I could reduce significantly the power consumption if I automatically switch off the server every night. I am using it also to do a distant backup of another computer, but I could setup the BIOS to switch it on every night to do that, if it is not already the case. The only thing I would need to do is just to switch the server on, whenever I want to print something or hear mp3’s, which is not too bad. The server would then switch itself off at night, after doing the backup.
• If I want to use XEN, I should compile my own patched kernel (for XEN) and tune the power management options to get the same consumption as on the stock kernel.
• I could try to tune further the kernel options, which I am not sure that I am going to do, as it is much more convenient to use the stock kernel than to use a self compiled one (e.g. for updates).
• I could try to find a way to cut off the consumption of some other electrical devices, which are most of the time not used or in standby mode, but do consume power anyway. Like for instance the laser printer (standby 14 W), the external backup hard disk Seagate 500 GB 7200.10 (standby 12 W), the wireless access point WRT54GL (always on, 14 W) or the cable modem (always on, 12 W). Not sure how I can do that. Of course I could plug some of these devices in a multi socket with a switch, but I would need to turn it on each time I want to access the internet using my laptop and turn it off afterwards (in addition it’s not compatible with my automatic distant backup). Not very elegant. I guess I will have to think about that issue.

Additional links:

• How to reduce power consumption Nice howto based on Linux with other options presented.
• Ubuntu forum post Use cpufreqd to tune CPU frequency
• Ubuntu forum post Which module to use for cpufreqd