Getting an energy efficient small server

2009-12-29

For mirroring my backup drive, central data store for devices, music playing and a webserver for experiments, I'd like to run a small server at home. I want this server to be energy efficient, easy to modify, robust, silent and run customizable free software. It should have at least 500 GB of storage, but 1 or 1.5 TB is better. You can buy very low-energy computers such as the Fit-PC 2 (6 watt) or the Linutop 2 (8 watt). Energy costs for machines that run constantly can be roughly estimated by doubling the power draw in watt, so running a device that uses 8 watt constantly costs about 16 euro a year.

Until recently the computer I used most was a Dell X1 Latitude laptop. That machine is now 4.5 years old. At the time, I chose it because it is a laptop with no fan and hence very silent. It is still better than any atom based netbook. So I would like to use this laptop as a server. UPS and screen are integrated which is a nice plus. The machine has a 1.8" disk built in. It is not possible to replace it with a disk of at least 500 GB. I wanted to know the energy cost of adding more storage to the X1. So I did some power measurements with an 2.5" external disk (Toshiba, 160 GB) and a 3.5" external disk (TrekStore 500GB). I measured on my current main laptop, a Lenovo X200s too.

Lenovo X220s (console, idle, low brightness unless otherwise specified)
Adapter only: 6 W
Console, low brightness: 19 W
Console, high brightness: 21 W
100% cpu and high brightness: 40 W
mounted 2.5" disk: 24 W
active (dd) 2.5" disk: 28 W
mounted 3.5" disk: 37 W
active (dd) 3.5" disk: 41W

Dell Latitude X1 (console, idle, low brightness unless otherwise specified)
Adapter only: 0 W
Console, low brightness: 15 W
Console, high brightness: 19 W
100% cpu and high brightness: 23 W
mounted 2.5" disk: 17 W
active (dd) 2.5" disk: 21 W
mounted 3.5" disk: 32 W
active (dd) 3.5" disk: 37 W

The 2.5" disk uses USB for power. The 3.5" disk has a separate adapter which is included in the power measurements. The device used for the power measurements is a DEM1379.
The idle 3.5" drive uses 13-15 more watt and the active drive uses 13-16 more watt. The difference is as large as power usage of the entire server. So I am now wondering if there are more energy efficient external 3.5" drives.

Comments

display off?

It probably makes more sense to measure long-time energy consumption with the display off, as it will likely be off most of the time you have the server running. Displays usually consume a couple of watts (you see this effect already comparing high and low brightness settings in your data).

Also, play around with the power management settings for the disk. Modern Linux kernels have USB autosuspend (switches off the USB stack when not in use), which can save another couple of Watts and of course harddisk power management. IOW, let the machine run idle for a while (I assume a backup machine will be most of the time) to wait until USB chipset have been switched off and the harddisk has spun down, and measure again.

Re: display off?

Turning off the display gives an extra 2 W less than low brightness. Managing power settings for USB stack and external USB disks is not trivial. Will the USB stack come back up when disk access is needed? Ideally, the machine would do something like this:

- take decision to go into lowest power mode with active CPU
- spin down all disks (with hdparm or sg_start)
- turn off USB stack

and the reverse when disk access is needed. The linux power management landscape is however complex enough that I could not find a simple way of setting this up yet. Alternatively, turning off the USB stack would spin down the external disks. If that works (unlikely, see below), a disk like the Samsung Story Drive which uses less then 1 W when not connected to USB is a good option.

When experimenting with spinning down the drives via USB with
echo suspend > /sys/bus/usb/devices/1-1/power/level
the kernel will start reporting IO errors. In other words: putting a USB drive in suspend mode is a bad idea unless you have unmounted it. Perhaps there are clever power management scripts that can do this in a safe way.

power/price/size

For $99 you can get a Sheeva Plug which uses 5W. Also consider running your root partition on a flash drive (usb stick/sd/cf/etc) so your hd wont spin up as much. Another very good option is any MacMini made after Jan 2009 as they use only 13W and have a full x86 intel in them.

Re: power/price/size

The Sheeva Plug from http://plugcomputer.org has only one ethernet and one usb connector. That is insufficient for attaching storage and audio out. As for MacMini, I want to support companies that produce open hardware and software. I've now chosen for a Samsung Story Drive 1.5 TB since it has apparently good power saving features. Also, I got wake-on-lan-from-off working so I can turn the machine on on demand. I did not figure out how to do the same trick from suspend to ram. The one is controlled by the bios and the other by linux.

usb hub

The sheeva development kit has one usb, one ethernet and one SD on the side. You can plug a usb hub into the one USB port to get multiple attachments. For me it was all about bang for your buck, at 5W and under $100 (it was even $89 for a short while) compared to the old desktop "server" I had running 24/7 it will pay for itself in about a year.

shuttle

I've been looking for something similar; seems Shuttle is pretty active there.

I just ordered this one before Christmas; http://au.shuttle.com/product_detail.jsp?PI=1241
One you might like is this; http://au.shuttle.com/product_detail.jsp?PLLI=917&PI=1322