|Are you looking to have the two drives work together in a RAID 1 configuration or are you trying to keep an exact duplicate copy of HDD-A on HDD-B.|
I don't think you can set USB drives up on a RAID controller. However I use an inexpensive backup program called Syncback SE that offers a backup type called "Mirror". I created a profile that is always running on my server and whenever changes are made to HDD-A Syncback (by way of the profile I created) makes the same changes to HDD-B.
Is this what you were thinking of?