Cannot add HD Partition
I have a 3TB Hardisk for my 27 inch iMac. I have added a partition to the current Macintosh HD and divided the storage space to :
1. Macintosh HD - 1 TB - Mac OS Externded (Journaled)
2. New HD - 2 TB - Max OS Extended (Journaled) ( Use as Storage for working files and resources )
The Macintosh HD already have softwares and programmes installed. Reading from other sites, I can partition even there's data on it because it will just dividethe drive into 2. So I use Disk Utility > just click on the add "+" button to divide Macintosh HD to above partition. But the options button is greyed out. After that a message appears " Click to Apply to apply changes. To make more changes you must first apply this change ".
After clicking apply, the partitions have been divided to two but I could not add another partition for New HD.
Is there a maximum partition for the HD? Or does this problem occur because I already have data on the original Macintosh HD?
iMac, OS X Mountain Lion (10.8.2)