First, do not use WiFi when copying a large amount of files to the My Cloud. Connect the computer to the router with an Ethernet cable. If at all possible make sure to use Gigabit Ethernet connection when connecting via wired. Next see the following thread on copying speeds.
As to the USB device not being recognized by the My Cloud. When a USB device is plugged in and properly mounted by the My Cloud OS it should create a “Share” that is listed both under Shares on the Dashboard and is accessible by Windows File Explorer and Macintosh Finder. If the Share is not showing up, then check the USB device name to ensure it doesn’t contain any special characters. Use only basic letters and numbers, avoid using spaces or underscores just to be safe.
For some users (myself included) certain USB devices were not properly recognized and mounted by the My Cloud. When connected the Dashboard USB icon would indicate 0K for the device. In my case it was the format of the USB device, a Toshiba 1T external USB hard drive that was the cause. I had to reformat the USB device before the My Cloud would properly mount the device.
