This might help → http://www.wdc.com/wdproducts/library/Flyer/ENG/4178-705183.pdf
Do note that Mirror is slightly cheaper than comparable capacity EX2 but as far as I know, the hardware is identical (processor and memory). But Mirror also doesn’t come in a diskless model but the EX2 does (allowing you to start your NAS cheap by buying and instaling just one drive and running it in JBOD…buy a 4TB, or even 5 or 6TB now and buy a second one later). And from the chart I can tell the Mirror lacks iSCSI, IPv6 and Active Directory support. Otherwise, they are pretty much the same beast.
Based on your post history, looks like you already own a My Cloud so you don’t need info on that ( http://community.wd.com/t5/WD-My-Cloud/Remote-access-certificate-expired-security-warnings/m-p/734250#M14572 )
