If you use fdisk to create a partition on your disc that is larger than 2TB you will only see the first 2TB of the disc. Instead you should use parted.

sudo parted /dev/sdb

GNU Parted 2.1
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) mklabel gpt                                                      
Warning: The existing disk label on /dev/sdb will be destroyed and all data on
this disk will be lost. Do you want to continue?
Yes/No? yes                                                               
(parted) mkpart primary ext4 0% 100%
(parted) p                                                                
Model: ATA WDC WD60EFRX-68M (scsi)
Disk /dev/sdb: 6001GB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt

Number  Start   End     Size    File system  Name     Flags
 1      1049kB  6001GB  6001GB               primary

sudo mkfs.ext4 /dev/sdb1