I have an EX4 with two 4 TB red drives. They are configured with RAID1 set to mirror. I would like to add storage. What is the simplest way to add storage and retain my data? I was wondering if I should add two more 4 terabyte drives, but i would rather add an 8 TB drive and mirror that with the two fours that I have now if possible? I and not real familiar with RAID drives. So i need step by step instructions.