Thanks in advance for the advice. I've read some threads on this, but none that directly mirror my situation, so I figured I would ask.
First the hardware:
R510 running OMV all by itself.It has an H200 so it see's larger drives.
It has 3 146gb dell drives in a software RAID in OMV.
It has had an 8TB WD (shucked easystore) for a while. And its got basically all of our "stuff" on it.
I was using another 8tb easystore still in the enclosure for backup and cold storage.
I picked up a 10tb easystore now for cold storage, so I shucked the other 8tb drive and put it in the r510.
I want to extend the current 8tb to a full 16tb by combining the two drives. It would be great if I can do this without loosing any of the data on the primary drive. But if I need to I could back it all up and then write it back again.