Does this help?
How to partition a Hard Drive:
I am having the problem mentioned in this article but the solution is not working for me since - when I follow all the steps and try to re-partition the external HD - I get the error message:
Particition failed with the error: Could not unmount disk.
Trying to reformat a BRAND NEW OWC external HD with 3TB of space, connect via Firewire 800.
Yes, thank you!