Just installed 4 TB HD - only able to use 2 TB

So, backstory: I have an otherworldly large iPhoto library that my wife would like to keep all together as sort of a master library of sorts. She is comfortable with that interface and has resisted the move to Aperture / Lightroom. I prefer to keep my photography projects nimble and manageable - and I do have LR for that purpose. Nevertheless, the iPhoto library is nearing 300,000 photos/videos and is nearly 2 TB in size. Conveniently, this library lives on a 2 TB drive in a Mac Pro (Mid 2012, I think it's the 5,1 model).

As photos continue to be taken, and need a place to live, I purchased a 4 TB drive to use for this purpose. I cloned the 2 TB drive to the 4 TB drive using Carbon Copy Cloner. We were then able to view our library on the new drive, we were able to download new photos to the same library, and all seemed fine until the library reached almost 2 TB in size. Now I receive error messages when I try to add new photos (not enough space on target disk).

I have checked disk utility and the disk is formatted as Mac OS Extended (Journaled) and is recognized as a 4 TB drive. I tried to copy new files to the disk using Finder and I get an error message that there's a problem writing the files due to disk space.

Any idea what I can do to help use the full capacity of this drive? The iPhoto version is 9.5.1; I'm using OSX Mavericks (10.9.5) which is why I posted here. Hope this is the right place to ask.

Thanks in advance for your thoughts...
C

PS Have lots of backups by the way, on- and off-site.

Thanks. That's what I thought I had done.
Bottom of Disk Utility looks like this:

If I have not formatted this disk properly, can you walk me through how to do so?

Answers to prior questions:

Hit Get Info; After Format it says Mac OS Extended (Journaled).

Yes, Set partition tab to one volume.

And finally, will try reformatting as drambuie suggested. Quick question: what's the best way to go back and re-format this disk - use disk utility and Erase function? I will just be re-loading the same data.

Ok. New problem:

I attempted to format it in Disk Utility using the standard GUID partition map and encountered a strange problem. Disk Utility formatted it using a Logical Volume Group (LVG) instead of GUID.

Furthermore, Disk Utility subsequently refused to allow me to reformat or repartition this drive. The Partition Layout drop-down in Disk Utility is greyed-out. I seem to be stuck with a LVG drive.

Disk Utility: Version 13 (450)

How can I remove the Logical Volume Group partition scheme and reformat this drive as GUID?

Here is what I got after the first terminal command.
What should I type for the next command?
Sorry, confused.

Tried and got this:

WD Green (don't have serial number on me).
Thanks - and let me know if you have any other ideas.
C

PS incidentally, does it look like I entered the termial command properly? I was a little confused as to which volume ID to use...

Update:

So after scouring the interwebs and discussing this issue with various tech-savvy friends and acquaintances, I was able to re-format the hard drive. I have an old Mac Pro 1,1 (love that old horse!) I use for a home studio setup which is running Snow Leopard. It is running Disk Utility 11.5.2. I was able to re-format my 4 TB drive as GUID using this version (I had been unable to do so on the newer Mac Pro (and newer Disk Utility version).

Right now I am trying to copy the old iPhoto library directly to the newly-formatted HD. Once that's finished I will try again to add more photos to exceed the 2 TB threshold I was unable to surpass previously.

Fingers crossed, and thanks to all (here and elsewhere) for your thoughts and advice.

Successfully reformatted disk as GUID, but still can't load data past the 2 TB threshold. So I still have a 4 TB drive that thinks it's a 2 TB drive.

Anybody have any new thoughts on the topic? I would have thought a fresh reformat in Disk Utility would have solved the issue. Nobody else having this problem out there?

Now I'm cranky.

- C

Get Info listed it as a 4TB drive; 1.98 used; 2.01 available.

No big files; Disk Utility thinks I have 2 TB free as well.

But I may have had a breakthrough. Put the HD back in the old Mac Pro 1,1 and I was able to drag and drop files to exceed 2 TB. Now it's back in the 5,1 and I'm able to put more stuff on.

Not sure what did the trick; may have been the reformat to GUID (although first try with data on the 5,1 failed). Maybe needed a re-start in between tries. No idea. But it's working now and I'm gonna run with it.

Thanks for the help!