You might imagine that the disk would write-cache only an amount of data that it could write to the surface with the energy stored in its capacitors after it de

You might imagine that the disk would write-cache only an amount of data that it could write to the surface with the energy stored in its capacitors after it detected a power failure. That's exactly what I assumed, at least for high-end disks. Any idea why they don't do that? It seems like a pretty trivial hardware feature that would save an awful lot of software complexity.