I did a full format the other day which took around 5-6 hours on a Seagate 3TB HDD, yesterday I used it for maybe 1 picture and that's all I used it for.
You should always perform a "full initialize" on a new or used HDD when placed in a foreign system. It is particularly important
to perform a full initialization if you are placing this drive in any striped array (RAID 5 , 0, 6, 10, 50, 60...)
If you are creating a pass-through or simple drive (single drive of 3TB), you can get away with a fast initialization, but what's the hurry?