We haven't included them in this round-up, but check out our picks for the best NAS hard drives ... Right now, the biggest portable hard disk drive has a capacity of 6TB; meet the WD My Passport ...

2014 - The very next year, Seagate introduced 6TB hard drives that don't use helium. They were cheaper, but used more power to operate at higher temperatures. 2015 - Finally last year, HGST outdid ...