Maybe it's a wrong suggestion, but I recently acuired for my "small business" an XIV and all peaople are more than happy with it. It may be way beyond over the top for your needs but for huge amounts of storage you need different calculations for sefety and redundancy. So when you actually need 9TB I would never buy storage hardware which could hold less than at least twice that much. Also access and IOPS to that data might be important. NAS systems tend to scale not that well if you have many users doing heavy lifting. So a SAN would be much better.
But now we are talking enterprise hardware with FC or iSCSI connections. So it really depends on you budget. If you can afford loosing all data and hardware and build up everything from scratch in days with a previously made backup, than a NAS build for home-use should be fine.
Also it should be common sense that if the data is important it should never be backed up on another harddrive, at least not at the same location. I just had a custome with a major power and UPS fail who lost his main storage and his backup on his NAS