I learned about the possibility a good decade ago when working on Oracle. For high performance use we used to have two areas:

- one small SSD-backed area where new inserts happened (Server class SSD was new and relatively expensive back then.)

- one (or more) areas for permanent storage, based on ordinary disks with good storage/price

Then we had processes that processed data from the SSD Pool and wrote them to long term storage asynchronously.

Edit: I should say I was very happy to find the same feature on Postgres, Oracle is a real hassle in more than one way.