The OP indicated in a prior post what the problem/solution was for in their case and it didn’t appear to have anything to do with the USB drive not getting enough power.
http://community.wd.com/t/mycloud-4tb-cant-recognize-external-usb3-0-hdd/181050/31
Adding a powered USB hub or using a split USB cable to provide additional power via a second USB port is one troubleshooting step people should try if they are having problems with external USB hard drives not mounting when attached to the My Cloud’s USB port. Sometimes hardware could be slightly out of spec.
On a side note, while the My Cloud User Manual indicates one can attach up to seven external USB hard drives using a hub, we’ve had prior discussions where people have trouble using more than four devices. Some discussion on that issue can be found in the following thread:
http://community.wd.com/t/my-cloud-and-usb-hub-powered/168885
In that thread I mention how I had trouble with a seventh USB device sometimes mounting as 0K while using a powered USB 2.0 hub.
