Update: I’ve since built a box with a mobile atom CPU which fares much better, as described in this post.
So I was all fired up to lower the power consumption of sandeen.net, the humble server upon which you read this blog. (And thank you for that, by the way. You can count yourselves among the 3 finest people on the internet.)
I decided to swap out the old AMD Athlon for an Intel Atom – you know, that low-power, lower-performance wonder-chip from Intel. I ordered a Gigabyte GA-D510UD from newegg.com, for $90… it looked interesting because it had 4 SATA ports built-in, which should suffice for any amount of storage that I’d likely have connected directly to it.
sandeen.net draws about 51W, which is really not too bad considering there are 2 active drives in it (a mirror) and one sleeping drive that gets backups occasionally. It’s a AMD Athlon(tm) 64 Processor 3400+ in an old Compaq SR1710NX that I got cheap 5 years ago or so, and updated the cpu, memory, drives, etc… These new low-power Atoms must be really great then, right?
So it gets here Friday, and I’m all excited… I take down the server, plug it in, and well, first off RHEL5 was not happy with it, bringing the drives up as /dev/hda, /dev/hdb… (remember those?), and and after a bit of fiddling to get the config right I decide to just put things back as they were, and play with the board offline. Before doing so, I check the Kill A Watt [amzn] … hm, still 51W. Odd. Hopefully a newer distro will do some magic power stuff and make it all better. It’s an atom right? Low power and all?
So I put the RHEL6 beta on it, and get it all fired up, and re-check … hm, nope, still 36W or so with a single drive, subtract out that 8W, the board is pulling around 27W. This is not the low power I’d hoped for! So I start digging – oh look, the chip doesn’t support any P-states, and only 2 C-states:
Cn Avg residency P-states (frequencies)
C0 (cpu running) ( 0.3%) 1.67 Ghz 100.0%
polling 0.0ms ( 0.0%)
C1 137.5ms (99.7%)
And sure enough, checking the Intel docs, only the chips designed for mobile use have the nice power features.
In short, the shiny new low-power Atom sure appears to use just as much power as my 5-year-old run of the mill AMD Athlon64 (in a low P-state, granted). Sure, at full-tilt maybe it’s using less, but it runs at full-tilt all the time and my Athlon is able to throttle back almost all the time.
I’ll eat the restocking & shipping and send this thing back to newegg, bitterly disappointed.
I have higher hopes for swapping out the hard drives (one leg of the mirror is dying) to WD Caviar Green drives – I can save about 8kWh/month with those if the specs are accurate. :)