Using my Amiga 4000D, coincidentally, I just brought home 160GB IDE drive. HDToolBox detected it as 127.9GB, but the partitioning facility only sees 7GB.
This is the same system which has been partitioning and formatting 40GB drives no problem.
It's a Quantum with a Cap Limit jumper, and I haven't played with that yet (gotta move the Amiga off the dining room table per the female companion unit. :-))