I found this in the WD My Cloud Userās Manual Page # 116
Hope this answers yoru questions:
"When you attach a USB drive to the WD My Cloud deviceās USB 3.0 expansion port, it becomes a network drive. Now the USB drive has the following capabilities:
ļ® When you connect an external USB drive such as a WD Passport, a memory stick, or a camera to the WD My Cloud device, you can access it with Windows Explorer or Mac Finder.
ļ® The USB drive can serve as a target for backups in WD SmartWare, Windows, or Time Machine.
ļ® You can map the drive as a user share drive (Windows) or an alias (Mac).
ļ® If a WD external drive has been locked, when it is attached to the WD My Cloud device, it maintains that security and can be unlocked or relocked using the Dashboard.
ļ® You can attach a powered USB hub to the external USB port and attach up to seven USB devices to the hub."