[throwaway81523]

There used to be battery backed ramdisks with SATA interfaces. Are they history now? These days it would be NVMe or whatever, of course.

[jakedata]

Radian makes ultracapacitor backed RAM cards with flash backup that appear to be NVMe devices. They do a nice job for things like Write Ahead Logs and ZFS ARC/ZIL. They offer effectively unlimited write endurance with a tradeoff of cost and capacity.