Since the inception of solid-state drives (SSDs), there has been a choice to make—either use SSDs for vastly superior speeds, especially with non-sequential read and writes (“random I/O”), or use legacy spinning rust hard disk drives (HDDs) for cheaper storage that’s a bit slow for sequential I/O1 and painfully slow for random I/O. The idea of caching frequently used data on SSDs and storing the rest on HDDs is nothing new—solid-state hybrid drives (SSHDs) embodied this idea in hardware form, wh...