Huawei may have used a very clever trick to make hard disks use less power — spin-on-demand disk drives may well compete with tape on performance, but at what cost?

We have. Spinning down disks not being accessed has been a thing for decades.

But it's rarely used, because even if you the user aren't reading or writing files, all the background systems are still using the disk. And spinning up and down is more west and tear on a drive than constant spinning.