Swapping data between 2 hard drives on the same machine

I have a 2TB Mid 2010 Mac Pro. I've added a second 2TB hard drive. My 1st HD is full, mostly with (1.6 TB of photos.) These photos are stored in a Lightroom Folder. The LR folder will open to the same base folder on both HDs, but is apparently all stored on the first HD. I'm trying to figure out how to move all (or part) of the photos to the second hard drive to free up the space on the original hard drive. I've tried starting a new folder on the second hard drive ( outside of the original LR folder duplicate) but that folder also shows up on the original hard drive, so the data is not eliminated on that drive. Any suggestions would be greatly appreciated!

Ok Backup...

What you want to do is transfer your lightroom projects from one hard drive to another then delete them off of the 2 TB to free up space correct:}