I have a “My Cloud EX2 8TB” and “4TB My Book”. I set the “My Cloud EX2 8TB” in RAID 1, then the device got the capacity of 4TB (with data mirrored across two discs). The problem is that the use of graphic that appears on the main page of the control panel just showed 8TB. I was about to open an RMA for believing that the unit was in trouble until, by chance, I discovered it was not a problem. My unit “My Book 4TB” was connected to the USB port of the “My Cloud EX2” and the chart was showing 4TB of “My Cloud EX2” ADDED to 4TB of “My Book”. I wish there was some setting on the control panel that allows the user to choose whether he wants the devices attached to USB ports are added to the total storage capacity OR NOT.