There are a few things that you need to do to get this to work. First, after physically connecting the drive, run
dmesg to see the name of the node in /dev. You should find something like this:
[ 5155.744879] usb-storage 1-1.4.3:1.0: USB Mass Storage device detected
[ 5155.753654] scsi host1: usb-storage 1-1.4.3:1.0
[ 5157.013418] scsi 1:0:0:0: Direct-Access ST4000DM 000-1F2168 PQ: 0 ANSI: 6
[ 5157.015712] sd 1:0:0:0: [sda] Very big device. Trying to use READ CAPACITY(16).
[ 5157.085733] sd 1:0:0:0: Attached scsi generic sg0 type 0
sda is the /dev node above, and you can see that it is there via
Assuming this is a new drive, you may only see
/dev/sda (or sdb or whatever the node was named), while drives with partitions will have
/dev/sda1, where sda1 is the node for a partition.
With an unpartitioned disk, you will not see it listed if you execute
fdisk -l. So you need to add a partition.
fdisk is not the easiest tool for the job in this case, because you need to use the GPT partitioning scheme.
fdisk will try to use MBR. But because of the way block addresses are stored in MBR, it is only able to index 2.2TB worth of addresses. That's why your drive looked like a 2.2TB drive to the OS, rather than 4TB.
Do this next:
sudo apt-get install gdisk
gdisk will let you create a GPT partition. Type 'p' at the prompt to list any current partitions. Type 'd' to delete partitions. Type 'n' to make a new partition. Assign it the number 1 when prompted. Type 'w' to write the changes. You can see your partition now using
fdisk -l. I'll assume it is named sda1.
With a partition in place you need a filesystem. To accomplish that:
sudo mkfs.ext4 /dev/sda1 -L gargantua
The -L option allows you to set a volume label. I used 'gargantua' for reasons. The .ext4 gives us an ext4 filesystem, which is recommended for the Pi.
Now that you have a partition with a file system, you can mount it:
mkdir /home/pi/drives/gargantua # or wherever...
sudo mount /dev/sda1 /home/pi/drives/gargantua/
df should show you that you have 4TB available and that the drive is mounted where you mounted it.
If you want to automount the drive at boot, you can use the GUID or the volume label. I'll use the label:
sudo cp /etc/fstab /etc/fstab.bk
sudo nano /etc/fstab
You need to add this line, or one more suited to your purposes to
LABEL=gargantua /home/pi/drives/gargantua ext4 defaults 0 2
The Wikipedia page on fstab gives decent examples and descriptions for editing fstab, if you need more information.
And that should do it, you have a very very big drive that mounts to the same location whenever it is attached to the Pi or its USB hub.