Great to see larger HDD's. Should be fantastic for home NAS users as my self. I currently have 4 x 14TB drives in an expansion unit attached to my QNAP TVS-1282. Would like to thank Western Digital, Seagate and the other HDD's manufacturers not mentioned for all the great work in the mass storage area. Long live the mechanical HDD!!!
Seagate has had a "SSHD" lineup for a while. Platter drive with a small SSD cache for things like boot up or commonly used files.
In my limited experience, they worked well speeding up boot times, but the laptop drives weren't very reliable. It would occasionally flush out the cache entirely with large read/write operations (eg installing a new game) and the next bootup would take an eternity.
Then SSDs became way cheaper with similar amounts of storage, and that became the no-brainer way to go.