In case of Seagate's Kinetic Drives, one core was used by the controller, the other 'extra' CPU was used to manage a Key value store on the driver. These were ARM processors. I don't think they make these themselves.

You would be wrong. I work with guys who used to do SoC design for both Seagate and WD.

This is how WD was able to jump to RiscV so quickly; they didn't have any suppliers they needed to negotiate with, and the market for CortexR style in order, single issue, fully pipelined real time cores is sort of a commodity.

Well, that's why I was asking. Thx!