USB HD goes to sleep forever

I’ve got a usb HD hooked up to my wd tv live hub and the thing works fine for a bit then goes to sleep and won’t wake up.  I either need to reboot the wd tv or unplug / replug the usb hd to get it to work again.  

Ideas?

I wishI I  bought  Seagate. They do not have permanent spin off mode. This is not what people need.