I don't know what you mean by a "3T partition".
There are many partitioning tools for Linux. To partition a drive that is in use, it is better to use something on a liveCD---eg GParted. GUI tools such as this are pretty self-explanatory.
The standard command-line tool is fdisk. It is fast, and has a limited help function. "man fdisk" for details. For kicks I just downloaded parted--it looks to be more powerful than fdisk (note that GParted is the GUI front end for parted.)
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