As of 2014, the world's largest hard drive is Western Digital's Ultrastar He10. The helium-filled drive is the first to hold 10 terabytes of storage.
Western Digital announced the arrival of the unit in September 2014. The announcement came just weeks after Seagate introduced an 8 terabyte air-filled drive, occupying the top spot for a short reign. The He10 utilizes a technology called HelioSeal, which hermetically seals helium inside the hard drive, and does not allow air or contaminants to get inside.
Also worthy of mentioning is IBM's 120 petabyte storage drive, stored at a facility in Almaden, Calif. Though it is significantly larger than any single hard drive, it would not qualify as a comparison, because it is actually built with 200,000 hard drives working together.