Just a note to anyone using OMV on a Raspberry Pi, I would highly recommend BerryBoot software. It places a small handler on the micro SD card that will install operating system on any connected USB hard drive. It allows you to partition, format, and install multiple operating systems on the attached hard drive (or even on the SD card itself) and boot from the image on the hard drive instead of the SD card.
Booting is MUCH faster than from an SD card.
It comes with a menu with nearly all the operating systems you would need, including Debian, OpenElec, OMV, Android, etc. Just pick the ones you want to install, and it pops up with a menu at boot time so you can select which image to boot from... Also has web server, terminal program, and memory test software.
Very handy, and seems to work well. http://www.berryterminal.com/doku.php/berryboot