Hi I want to build server, I would like to have it to have power consumption at load max 30Watt, lesser is better. I need there only: HD(can be SSD or CF), CPU, RAM, power supply. What CPU, Motherboard(chipset) you recommend, RAM, power supply? Thanks a lot.

What will this server be used for?

If you want the max power consumption at load to be 30 watts, you really only have two choices: a fairly extreme underclock + undervolt of a CPU like an AMD Sempron or Intel Celeron; or, get a wimpy CPU such as those from Via, AMD Geode or Intel Atom.

Check out this thread. Using a PicoPSU, a compact flash card as a hard drive, and underclocking + undervolting a Sempron LE-1250 down to 800 MHz/0.85 volts, I was able to reach idle power consumption of around 22 or 23 watts. I did very little testing of power consumption at load, but going from memory, I believe this setup was right around 30 watts at load. Don't hold me to this (because my memory is poor), but I think that I was able to have power consumption under 35 watts at load with a similarly undervolted + underclocked 5050e CPU.

For these super-low power systems, the current recommended PSU is the PicoPSU.

Be careful with the Atom motherboards though: most come with a northbridge that is not very power efficient. One exception is the Intel D945GSEJT, which is based on the mobile 945GSE chipset, which is low power. I don't have any personal experience with this board, but it looks nice if you want something decent and low-power.

I just bought an Alix2d3 from PCEngines. I use it as a firewall/gateway/NAS device. It pulls only 5 watts at idle. I didn't test how much it pulls at load, but it certainly can't be more than 10 watts.

Yep, the D945GSEJT uses the same 945GSE chipset used in netbooks. My netbook pulls less than 20W at load and that's with the LCD so I expect a D945GSEJT-based build with minimal parts will use the same or less power. Another nice thing about that specific motherboard is it already comes with onboard PSU. You just need to buy an (efficient) external 12V AC-DC adapter. One downside for me is it requires laptop memory. I've got a bunch of spare DDR2 DIMMs but unfortunately, no DDR2 SO-DIMMs.

Not sure if it's comparing apples with apples, but this chap Adam has built and documented his dual core atom build (mini itx, MSI IM-945GC though not available anywhere in the UK). Like you (and alot of us) he is after a low power always on server.

The reason I posted is because he has kindly published his power consumption figures. Respect to Adam for his work:

http://www.adamretter.org.uk/blog.xql

What's interesting, is using an ATOM he ends up with 40W+ idle. Matt's solution is in the low 30's based on 5050e. All good reading (thanks Adam if you read this).

I may have skimmed that article too quickly, but his 40W+ idle number includes his four 3.5 inch data drives, right? My 30W was sans any rotating disks.

Yes. I must have skimmed it even quicker. Thanks Matt, nice spot. Sorry if I have confused any one, both projects in their own right are educational reading.

I already have intel atom board, and I am not completely satisfied. The purpose of that machine is server running virtualized Mikrotik RouterOS. Or just Mikrotik RouterOS. I know that alix boards, they look decent, but I need 4 ethernet ports, 4 wifi cards in one PC. Traffic is about 10Mbit/s. Max traffic 50MB/s. A lot of firewall rules, QOS(so it is pretty hardware hungry).

If you're not satisfied with Atom, best solution is AM2 motherboard that supports undervolting + Sempron. With just a single HDD (especially 2.5" or CF) and PicoPSU, you will have no problem getting < 30W AC.

I've recently bought a D945GSEJT, which I am very happy with. I'm currently running Ubuntu server 9.04 from an 8GB USB thumb drive, with a 1.5TB Samsung F2 5400 rpm drive and a USB TV tuner for Mythbackend recording. It runs at about 18 watts idle. If the HD is spun down it goes to about 15W - without the tuner it's 13-14W. If you want low power consumption, it's great for a server on fairly low loads.

I also installed a basic Gnome desktop, and it runs pretty well for web browsing etc without having to fire up my main PC.

I got it from linitx in the UK - see http://linitx.com/viewproduct.php?prodid=12472 at just over £100 with a 60W power brick. I'd recommend their service, which is excellent!.

I've put the board in the speaker housing from an old pure legato micro (http://www.pure.com/support/kb.asp?Product=VL-60692) hifi - it looks very good at the moment with 2 low speed 80mm fans where the speakers went, I might put some pics up when I've finished construction.