Seagate is looking to create its own law about the increase of density in its products, aiming to double capacity every 30 months on its hard drive families.  They may not be as fast and sexy as an NVMe drive, but for long term storage which you don't expect to be constantly accessed, the price is very attractive.  They will no longer be using perpendicular magnetic recording, with all lines moving to HAMR, which should allow them to create a 20TB or greater drive by 2020 and perhaps reach 100TB by 2026.  Other companies are investigating different recording technologies, which The Register briefly mentions here.

"Seagate has set a course to deliver a 48TB disk drive in 2023 using its HAMR (heat-assisted magnetic recording) technology, doubling areal density every 30 months, meaning 100TB could be possible by 2025/26."

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