Hello Matthew-- We use NAS units here to back up our digital collection and other vital data in triplicate; it gives us a little over 7 TB of storage. Since the implementation of this system in 2011, we've used a little less than half the capacity. Backups occur daily, weekly, and biweekly among the 3 units. This system works pretty well for us. Good luck.
Regards, -- Matt Wheeler, Photography Archives, Penobscot Marine Museum Archives (207) 548-2529 ext. 211