Hi, guys

I going to assemble home virtual server with several virtual machines (at least 2):
1. For web hosing, internet and file sharing, automating different tasks (one or more linux systems).
2. Programming, working with Microsoft Office, browsing Internet, watch movies (up to 720p) (windows).

Initially, I considered DN2800MT board, but it barely can spin up 3,5'' HDD (it provides only 1 A at 12 rail and my current HDD requires 2,3A when spin ups). Then I looked at Socket 1155. Here is my outline:
1. It will not be my main system so it's enough cheap solution - Pentium G620 with H61 chipset board. G620 supports Intel VT-x technology so I can install ESXi or KVM virtual machine manager.
2. System is planning to work 24/7 so I also planning to automatically underclock it at night, if possible.
3. Maybe even will be enough 60W DC-DC PSU with permanent undervoltng of CPU to build completely fanless system.
4. Most of time I will work at other place so I intend to provide web interface to manage my virtual machines (disk resize, make snapshots, power on/off etc). I heard that Proxmox Virtual Environment is good enough for this.

My question is simple - I quite new at assembling silent pcs and installing virtual servers, so would you check my plan for any weakness or problem.

If you're going to use it as an HTPC to watch movies, you'll want to install Windows as the main OS. On top of that, you can add VirtualBox or VMWare Player or whatever you'll like. You can use remote desktop to log into your windows and manager your VirtualBox instances. It doesn't really make sense for you to install ESXi. Regarding the DC-DC PSU: I wouldn't really go that route, get a normal ATX PSU instead. For VM's, you'll want lots of RAM: get 2x 4G sticks at first, you can add the rest when your usage is up to it.

Try to keep it as simple as possible, as everything that can go wrong, eventually will

I urge you to reconsider... what would be the point of playing videos in your VM?
Basic VMs have I/O issues. They're acceptable in many cases but videos and of course 3D games are likely to be put an undue strain on your box. And for what purpose?

Data integrity also requires particular consideration when using VM. Some of the easiest things you might want to do is to avoid using files in a file system running on the host as VM containers, disable some of the caching, pick a server board or get a decent UPS.

The kind of underclocking you can do with a desktop Sandy Bridge isn't going to affect your idle power consumption much. The point is to curb the power consumption at load.

Desktop Sandy Bridges are not designed to run without any fans. It can be done of course but I would not recommend cheap fanless solutions, especially for a server.

Your HD may not require so much power to spin up. With careful selection, you can avoid this situation anyway. I was able to run a 3.5'' drive on my DN2800MT but the lack of even the most basic VM extension would make it a choice basis for your project!

Thank you for your comments. I decided to check how fast virtual machine (VMWare 6.0) when playing videos.
I choosed simple 640x480 30 fps home video and played it in virtual machine and at host.
My small investigation shows that CPU load when playing video in virtual machine is about twice higher comparing same video at host machine. I think its because unavailability DMA support at virtual machine.
Anyways, G620 is guite fast CPU so I intend to check how good it will be when playing HD video in VM. If it fails, I'll make Windows as my host machine