An Intel Optane NVME SSD. <10µs latency for both reads and writes even at low queue depths. There are newer NVME SSDs with more IOPS, but only at high queue depths, and their latency is a lot worse. If you put your swap on your Optane drive, you can use hundreds of gigs of swap without making your machine unresponsive. Makes a great place to put a database too.

Check out this screenshot http://db48x.net/temp/Screenshot%20from%202019-12-09%2013-27...

See where it says “avio 3.53µs” and “avq 0.61”? That’s 284,000 IOPS even with nothing queued up. With any other drive you would be lucky to get a tenth of that at QD1. Even better, this is a mixed read and write workload; most drives are fastest when you are only reading or only writing.