USB remote HDD turn off/on

All drives can be told to spin down/up using commands over the bus connection, but it will depend on your router's management and filesystem if it gives you access to such features. The other thing that many drives can be configured to do is to spin down after a period of inactivity, but again, you need some management software to configure this.

Spinning disks up and down does cost significant disk life. You don't want to be doing this too often if you want the disk drive to last. It might save you a few watts, but for a single drive, that's going to be a saving of less than £5/year, for potentially much shorter disk life (depending how often you do it).

Andrew Gabriel submitted this idea :

Thanks, have you a link to any software which might support this please?

It will not be run up and down often, likely less than once per week.

Does it not spin down a minute or two after you unmount it?

Get one of these.

snipped-for-privacy@gmail.com wrote on 06/01/2017 :

It would be permanently plugged into the router, but no I have no I have not heard it spin up and down other than when its wallwart is plugged in. It is silent when running, but quite loud at spin up and down.