Having on going problems with Time Machine backups

[iMore Question]

I have a Airport Extreme 802.11 AC with a LaCle 3 Gig hard drive attached by USB. I have an iMac and a Macbook Pro that I want to backup. I often receive cannot find backup disk error message when backing up with either machine. Most of the time unplugging and then plugging back in the USB cable solves the problem until the next backup. This happens on both machines.

 

[Just_Me_D]

It's as if the connected storage device is put to sleep when not in use after a period of time and when you disconnect and then re-connect it, it wakes. Having said that, is there a setting of some sort that could keep it active or allow to wake when you're active on your computers?