i just noticed that my Titan Black wont load more than 3GB in its VRAM.
I attached a screenshot where you can see it says "Memory 6 GB", "Used 1419 MB" and "Free 1529 MB"
what doesn't make sense to me.
Do i miss a Memory limitation setting?

edit:

Same with a GTX 970, the sum of Used and Free Memory is different from the overall Memory.
It's allways like 50% of the actual Memory.
So i guess its not an issue of the GPU but octane/my system?
my system:
MacPro5,1 OS X 10.10.1
GTX TITAN Black
Octane Standalone 2.13
Octane C4D plugin 2.14
CUDA Driver 6.5.25, NVIDIA Web Driver 343.01.02f03
have a nice day,
Jonas