I have an 27 inch iMac (mid-2011), running Sierra. I want to backup the internal 2GB hard drive. Probably using Apple's Time Machine app. Which would make sense, a single external drive or RAID 1? I like the idea of a RAID 1 for it's redundancy and peace of mind. I was looking at getting the OWC Mercury Elite Pro Dual and stocking it with 2-WD Black 6TB or 2-Seagate BarraCuda Pro 6TB. Has anyone had any experience with these particular drives (or series)? Thanks!