Mediadevices power reduction quest Pt. 1: PC power hog
Optimizing my home’s multimedia capabilities is an ever ongoing quest. The good kind, except for my wallet. It currently consists of a Linksys E4200 v2 with USB connected NAS (Network Attached Storage), PopcornHour C200 with a 1TB internal drive, also configured as a NAS and a windows 7 PC, always on to run Plex Media Server to stream content from the two NAS drives to various (mainly iOS) devices. Both the energy bill and the environment are important issues and I got the feeling all these different devices running non-stop burn up a lot of watts. Ease of use, always being able to connect to my media and watching it in a variety of ways is paramount, but perhaps this can be achieved in a more ‘green’ way to! This blog entry will be the first of many about the power consumption optimization of my personal media systems.
In order to measure the actual power consumption, I treated myself to a Fluke 87 multimeter. Fantastic device. Very accurate and it has the capability to record the measurements to give an average over a long period of time. I constructed a powersocket adapter to splice in the meter to measure the actual current being drawn. This current multiplied by the voltage of the wall socket, in my case 235 volts, gives the wattage (P=V*I).
First up is the Windows 7 PC. Suspectedly a big powerhog. It’s a HP small form factor model with an Intel dualcore 2,7GHz processor. Nothing fancy but fine as a server/transcoder, even at 1080p, which is it’s main purpose. It’s running Plex Media Server (http://www.plexapp.com). For the ones who don’t know Plex, it’s a very powerful and easy to use media indexer, streamer and transcoder for images, music, videos and more. I use it to index music and videos from my two NAS drives, ‘direct play’ the content to my ‘direct play’ capable devices like my Samsung 40D8000 and MacBook Pro, or transcode video for viewing of my iPad, iPhone and systems outside of my locale network.
Transcoding uses a lot of processing power, which translates in overall power consumption. Let’s check that out first. A 1080p video file maxes out the processor and a current of 361 milliamps is being drawn. A simple calculation tells me 85 Watts. Not too bad. I’ve seen systems use up twice that amount, so it’s less then I expected. But 90 percent of the time the PC is idle or streaming without transcoding. It should use significantly less power. Wrong! Doing nothing, it still draws around 218mA. That’s 51 Watts! I’m shocked. A Mac Mini for example (not really fair, because it’s advertised as the most energy efficient system out there) uses only 14W when idle. Assuming the PC will be up and running for about 300 days a year, it’ll cost me around 85 euros annually. Not acceptable at all.
One obvious solution would be turn it off when not in use. But that’s not an option. I’m not a media-snob, but I DO want 24/7 direct access to my media from anywhere in the world. Wake-On-Lan might be the way to go, but bootup just takes too long. I want it quick and snappy! And there are issues with Wake-On-Wan (yes, with a second W) for use over the internet. WOW stability can be dodgy, but more on that later.
Then there is sleep/standby. Not to be confused with hibernate (hibernate writes the RAM to disc and then shuts down. Bootup is faster then a cold start, but still takes a while). Sleep/standby also needs the use of WOL/WOW to gain access to it, but it keeps the data in RAM by powering only the memory and shutting down everything else. Well, not everthing. There’s always some power going to e.g. the NIC. But surely, RAM can’t be that power consuming can it? I put the PC to sleep. 55 Milliamps. That’s still 13 Watts! That’s horrible. It’s basically turned off. Although only a quarter of the power used when idling, it feels wrong to burn away 13 Watts on… nothing.
Just for the sake of experimentation, I measured the currents for hibernate and complete power off. 51 and 50mA respectively… My jaw dropped. Fully shutdown, the thing uses 50mA or 11,75W, for just being connected to a wallsocket. At least the sleep/standby power consumption made sense now. Just 1 extra Watt for fast power on is not a bad deal. To put all in perspective, the current Mac Mini uses 1,16W while asleep and 0,23W when fully shutdown and in both cases, WOL is still fully functional. That’s only 10% of my power hungry PC.
In conclusion, for now, sleep/standby with properly configured WOL and WOW run from my iPhone is the best compromise for (almost) instant 24/7 access with a quarter of the idle power I used to consume. It takes the extra WOL step and about 5 seconds of waking up the PC before I can enjoy my favorite music or movie. I guess that’s doable. Now I’ll just have to restrain myself from running to the Apple store for a Mac Mini.
It can be tricky to get Wake-On-Wan to function reliably. WOL works by broadcasting the ‘magic packet’ across the entire LAN (unless otherwise configured). The NIC with the called on MAC then boots or wakes up the PC. Wake-On-Wan is a bit different. First there’s the need to forward a UDP port, usually 9, to get magic packet from WAN to LAN. But there will be no broadcast, because port forwarding only works to a specific IP address. You have to configure the main router by means of DHCP reservation or ARP (Address Resolution Protocol) to let the router know what MAC address belongs to what static IP while the actual system is not in use. Many people have issues with WOW working fine moments after the PC is shutdown, but after mere minutes to a full hour, WOW just stops working. This is due to the router clearing its ARP table and therefore losing the connection between IP and MAC. By assigning a static IP to your device and manually adding the IP/MAC combination to the DHCP reservation/ARP table, the issue can be resolved. At least, it did for me.