Since Mac includes BASh you can do it from the command line using rsync (the above mentioned RoboCopy uses rsync). The nice thing about using rsync is that it both only updates what has changed and it checks its work (using checksums).
I wrote a script for using it to run backups on my music server (also something like 2 TB of FLAC music):
Backup Script: A Love Story | A High-Tech Blech!
I use rsync to do all of my network transfers (for instance if I rip a new CD on my main machine I will run rsync across ssh to perfectly transfer the new music to the music server). I even use it to transfer film files to a USB stick (because if the file gets fragmented it can be difficult for my theater player to read the bits in succession).
