How long does it usually take to format a 2TB external HD using ext4 and gparted?
It depends. Are you just formatting, or formatting and wiping the drive? How is the drive connected? USB 1/2/3? Firewire? eSATA?
Are there other partitions that need to be cleared off first?
Honestly, its probably going to take a while, so be patient.
It takes 17 minutes and 16 seconds.
Using: Ubuntu 10.04 amd64; gparted 0.7.1; mke2fs 1.41.11; USB2; a Western Digital Elements 2TB drive. This is just for the format; the partitioning was done in an earlier step.
Your mileage may vary.