If you are looking for the highest capacity external hard drive, the WD My Book Duo 20TB is the only one that can be obtained, as it offers 20TB of storage space.
If you do not mind sacrificing part of the large storage space, you can configure the drives in a RAID array, so you have backup copies of your files if one of the drives dies.
This USB 3.0 drive has many of the features of a full-fledged NAS device (including a high price), and if you have a router with a USB 3.0 port you can use this as a storage device connected to the network in its own right.
The device, which comes with a two-year warranty, has 256-bit AES hardware encryption and automatic backup software (WD SmartWare Pro).
It is worth noting that the enclosure used is completely repairable and that WD sends the already preformatted disk for Windows users (NTFS).