yes it is ...
here are some examples of which ext. hard drives are best for PS4:
WD 3 TB My Book
WD 4 TB My Book
WD 6 TB My Book
WD 8 TB My Book
Toshiba Canvio Basics 1 TB
Toshiba Canvio Basics 2 TB
Seagate Expansion Portable 1TB
Seagate Expansion Portable 2TB
Seagate Expansion Portable 4TB
Samsung Portable SSD T3 500GB