I haven't gotten around to making a loopback cable, yet.
With the HP Mediasmart, the loopback plug is not going to do you any good. If you plug the loopback plug into the HP, you cut off your SSH session to the command line AND the web gui. (It's like going out on a limb and cutting it off.) Without the VGA cable hack and a USB keyboard / mouse combo, the plug can't be used.
It wasn't easy to install omv on it, it took a lot of trial and error. I booted my laptop with the omv installation media, and installed omv to a hard drive in a usb enclosure. Then moved that drive to the mediasmart and ran omv-firstaid to reset the network connection blindly. That's why my setup uses eth1 instead of eth0.
I was thinking of trying something like what you did, just to be able to use the MediaSmart after MS discontinued WHS. The HP is power efficient and it holds a good number of drives, but I didn't want to get trapped in some technical issue without the ability to boot locally, with a keyboard and monitor. So, I left it with WHS1 installed and used it's drives / shares as a cold back up. (I fire it up every other month or so, sync my current shares to it, and shut it down. I've been doing this for years.)
If you want to make the VGA mod, info files are attached. You can use a standard VGA video cable and solder the correct pins to an old pata hard drive connector, with 1 wire per pin. (You'll have to file the key tabs of the connector flat.) I wouldn't worry about the mouse, KB, serial on pins 13 and 15, +5VDC on pins 1 and 2, etc., on CN2. Just connect the VGA, pins 16-25 and 14 . You can, and should, use a USB KB / mouse combo. (Your call.) While it might not be pretty, you'd probably have to punch a hole in the side of the case.
But i did try something else and got the same result. I decided to try running omv in a virtual machine on my desktop. The install and all updates went fine. So I moved my pool drives to my PC case, and set up the pool and share. It ran great for about a day. Everything was much faster than the mediasmart, too. Plex loaded videos almost instantly. But I got home from work today to find my network down. I shut down the VM, and my network came back up again.
I was trying to rule out the aging mediasmart as the cause of the error. I'm not sure what I could be doing wrong.
I install OMV, run apt-get update and apt-get upgrade. When that finishes, I install any available updates from the updates tab in the web ui. Then set my static IP, mount my pool and set up samba. Install my plugins (sabnzbd, transmission, and plex). I'm not doing anything too complex that I would be messing it up, I don't think.
Let's think about this for a minute and recap. You're having a problem where your network goes down, with an OMV machine attached. Otherwise, your network is fine. (As I understand it.)
1. The problem occurred with two different OMV builds (even 2 different versions).
2. To the best of my knowledge, you're the first on the forum that has mentioned this type of "flapping" network problem.
(Other than some sort of strange router / OMV interaction.... But again, as you describe it, you seem to be the first.)
3. Your desktop is fine, or at least it's not causing network problems.
4. You build a VM on the desktop (a 3rd OMV build) and then (get this) you install your drive pool (a RAID 1 pair?) in your desktop.
5. After a time, the problem shows up again, on another hardware platform.
What's the common thread? The drive pool.
Here's a bit of speculation. Really a "WAG". (Wild A~~'ed Guess.)
The power supply provides various voltages that tie into the MOBO AND your hard drives. Internal sata drives use 12V, 5v, and 3v. If one of your drives' interfaces' is damaged, one of the hallmarks of ESD damage in CMOS circuity is intermittent bursts of low level static (errors). These bursts can also travel on, and contaminate, the various PS voltages. (3v being the most vulnerable of all of them.) If this gets to your Ethernet interface, static (garbage) could take down your network.
This "WAG" would be fairly easy to test. First, unplug the power and data connections (no connections) to your drive pool so they can't touch your desktop in any way. Fire up your desktop and the OMV VM. Let OMV run, and we'll see if it runs for a few days without incident.