Hi Migi
I don't know the answer but I'll answer the question
Well, not exactly.
My question is : Do you need USB3 card and drives for mirror ? The answer is NO in most cases. With USB2, the FIRST mirror will take time but the following mirrors will be very short and fast (unless you change or add huge quantity of files everyday).
Save the money and buy a bigger USB2 drive.
Now, if you want to use these USB3 drives as "data server" drives, than it may be interesting to have USB3. But, in this case also, an internal drive may be faster
Robby