Western Digital just announced the largest mechanical hard drive in the industry, a 15TB helium-sealed monster. Designed for data centers and cloud storage services, the 15TB HDD is intended for enterprise customers in need of densely compacted, reliable storage. Pricing and availability haven't been announced, but don't expect the drives to come cheap.
https://www.notebookcheck.net/Western-Digital-unveils-new-15-TB-hard-drive-the-largest-HDD-yet.346781.0.html