I generally agree but: > Anyway, today there are only 3 kinds of secondary storage worth caring about: flash (sector granularity, but no seeks), cloud (like S3

I generally agree but: > Anyway, today there are only 3 kinds of secondary storage worth caring about: flash (sector granularity, but no seeks), cloud (like S3), and archive (like Glacier). "cloud" and "archive" are not storage devices, they are network architecture, and a service. There is a whole lot to write about that, but this is not on the same layer. "The cloud" uses flash memory and spinning rust, and they need to care about how to get the best performance out of the hardware they use. Maybe there is not much left to discover, and maybe fewer people need to know about that, but it still matters. Same thing for "archive", with less flash and more tape.