JustinG
I have too done some experience with Raspberry Pi and also with RPi 2
together with OMV.
My discovery is that USB2 and the 100 Mbit Ethernet interface both
is the course of your and my speed issue? It simply doesn’t work
because of the weak HW.
Recently I bought a BananaPI board with a SATA interface and Gigabit
RJ45 interface. Together with a 2 TB 2 1/2" HD I have a max. 7W
NAS running OMV.
It's working almost as perfect as the Pro NAS I have bought in my
Computer shop around the corner.
Unfortunately BananaPi+HD+PWR-suply is the same price as a pro
NAS, but I can tell my wife that I build it my self, and she think
it was the cheapest solution ;-|
Also I'm very close working together with my OMV NAS 
I bought the BananaPI at the dx.com portal. At the moment you find
BananaPI at a price of $50 including an Acrylic box. Remember also
to order SATA and PWR cables for the HD (round $4)
You surely find a lot of other nice things to use you’re left over
RPi 2 for.