I would not use the WD Elements for continuous operation, as it is not designed for this. I recommend a NAS with a suitable hard drive (e.g. Sinology with WD Red hard drives). A hard disk always needs a power supply. For continuous operation, such as with a NAS, via an internal or external power supply unit or directly via the computer. It seems more important to me that the hard disks consume little power and are configured in such a way that they switch to "sleep mode" (power-saving mode). This can usually be set via a configuration menu.