Resizing HFS+ volume after cloning
This is really terrifying that the only answer suggest to overwrite your gpt table.

The correct and safest solution, with explanation, is from this comment.


download GParted-Live CD from http://www.gparted.org/download.php
boot from this CD
accept the suggestion to enable the full disk
reboot from mac OSX
try again – now you can resize it!


Explanation:

The only problem is the disk header which exists twice: at the beginning and at the end of of the disk. Somehow Mac OSX shows the real disk size, but is not capable to change the GPT size header and to relocate the second “header” to the real disk end.