Let me preface all of the following with this: If you are not comfortable with the linux command line I would avoid putting VirtualBox + MineOS+ on your unraid box. I started with just using VirtualBox on my Windows 7 64bit system and playing with MineOS+ inside of that before trying to get it working on my Unraid server.
Just install Vbox on Windows and install MineOS+ inside that.
If you follow the VirtualBox tutorials on this very forum to install VBox on your unraid server, you'll end up with a web UI interface into virtualbox, complete with a web console (or even RDP) to whatever virtual machines you run. Of course, once you get MineOS+ setup, you can SSH in to your server as well as use the web interface to manage your server.
I have made some customizations to how Vbox (and a lot of other addons for unraid) are stored and installed. Instead of having them packaged in gzipped tar files that have to be uncompressed every reboot of the unraid box, I have them stored on my fake cache drive (/mnt/cache2). I manually partitioned and formatted the drive for reiserFS (I think previously I said it was ext3, I was incorrect) and added commands to the unraid "Go" file to manually mount it on boot. I then have it create symlinks to directory structures on the mounted disk so that the files for virtualbox and other addons show up in the right places already preinstalled. This saves a huge amount of ram as VBox takes over 100MB fully installed. I also have 5GB of linux-swap partitioned on that 100GB fake cache drive and use the unmenu swap addon to enable it.
As for the MineOS+ virtualbox, I pre-allocated a 4.3GB (small enough so it would fit on a DVD+R) file on /mnt/cache2 (outside of the array) and used that as my Vbox hard disk for the MineOS+ install. I allocated 1GB to swap, 2.5GB for the backup partition(sda2) and 500MB for the system partition (sda1). I'm using the ramdisk installation for MineOS+. This is where it really shines.
I have a full craft bukkit server running Minecraft 1.5_01 (because 1.6x is horribly buggy and needs fixing) along with a whole host of plugins. I setup automatic incremental+differential backups every 10 minutes of all three worlds, auto backup pruning (keeps 72 hours of backups), auto mapping using the google map API every 4 hours (you can see this at www.kaijin.com
- pick world three or two, one is boring) along with an automatic encrypted public key protected rsync of the files up to the previous mentioned website, and daily safe shutdown and restart of the virtual machine (gives in-game warnings, saves everything, reboots). On restart of the virtual machine, it will restore all three worlds from the latest backup to the ramdisk and then start world three by default.
Considering that my entire Unraid box only has 2GB of ram on it and is running a Sempron 140 single core CPU, I think things run damn well. The swap space for both the MineOS+ and unraid box are needed to keep both from running out of memory, but I do not find swap is used all that often.
I just ordered another 2GB of ram for the unraid box and plan on giving 1.5GB of it to the minecraft VM and leaving the other 512MB to Unraid.
In terms of just trying to get the minecraft server itself to run on the unraid box, that's super easy. Install JVM and you are basically done. I decided to go with MineOS+ because of the ramdisk based install, built-in web administration and easy customization along with fully incremental and differential compressed backups and the ability to provide a level of protection between the internet and my unraid box.
Also, if minecraft crashes and takes down the entire VM, it shouldn't end up crashing the entire unraid box. I have had the VM crash and hard lock multiple times while fiddling with things and it never once made the unraid box blink.