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