Can not find the 2nd hard disk

My Cloud OS 3 Personal & Network Attached Storage My Cloud Mirror
1

My Hard disk cabinet(Yottamaster) connect with the Cloud mirror by usb, yesterday I installed the 2nd 8T hard disk in the cabinet(two 8T hard disk). But it can not find the 2nd hard disk in any case. So I let the cabinet connect with my PC, the two 8T disk is all good and I copy some movie to the 2nd one.
My cloud have 2 usb, one connect with an 8T external hard drive(Seagate)，one connect with the Yottamaster cabinet which has two 8T hard disk. And as I said, when they all connect to My cloud with USB, I can only find the external 8T and the first drive in Yottamaster.
Pls help !!!