I have two NAS Solutions, both using raspberry pis running OMV. First one is a single external USB hard drive acting as a buffer when it downloads my legitimately obtained media before transferring its data to the second NAS running two USB hard drives running RAID 1 for deep storage and streaming.
The single drive can power itself through USB. The other server with 2 drives have their own independent power supply. Look up WD EasyStore to get an idea of what kind of model they are.