The Windows system you are using only recognizes up to 2 TB. The System is using the old MS Dos based system.
MBR (Master Boot Record) and GPT (GUID Partition Table) are two different ways of storing the partitioning information on a drive. This information includes where partitions start and begin, so your operating system knows which sectors belong to each partition and which partition is bootable. This is why you have to choose MBR or GPT before creating partitions on a drive.
Now You cannot use the Disk Management system from your computer, if you are not given the option to choose which type of disk you wish to create when you first attach to a computer.
The Disk Management program will not list as below.
- After you install a new raw disk, open the Disk Management console to start a wizard that you can use to configure the new disk. The wizard includes options to initialize the disk as MBR or GPT.
Now you wish to choose GPT, BUT, this does not occur. I have a Laptop, which I connected the MyBook 3 TB to, and low n behold, immediately a Window pops up, and advised, if I wish to use the harddrive, I must choose which format I wish to use, and format and partition as required. So I choose GPT and format, now I connect to my computer and shows full 3 TB.
I would suggest you find a friend with a laptop, with Windows 7 to Windows 10 and connect your unformatted unpartitioned MyBook 3 TB to the laptop, and you will be able to format to 3 TB…