Ultra 6 configuration question

You might want to consider two Ultra 4 units. One would be your main server so the data would be accessible by any computer on your home network at any time without having another PC on all the time. The second could be set up to update it's data from the first using rsync (after the initial backup job running NFS). Then you could back up your critical/important data to an external drive on a periodic basis as you are doing now (similar to what I was doing, maintaining a baclup Passport in my desk - now a bank SD box since I've retired).

Remember - never trust your data to only one device. If you take digital photos, don't erase them from the camera until you have backed up the images on your PC for example. Redundancy in an NAS (single or double) is intended to be able to recover from a disk failure easily, it s NOT a backup plan.

I was seriously searching as you were about 18 months ago and considered the Pro, but wound up with two NVX units (replaced by the Ultra 4) for about the same price. Last night I came home from a trip, plugged in and turned on my UPS which then proceeded to power up my equipment (router, switch, modem, two NVX units and a printer which should not be on the circuit). My backup unit powered up normal, but my main one sat there with the fan running and no lights. First thought - unprintable. Second thought, I can run off the backup unit while I am working on the primary (I also do this when upgrading units), third thought try again. Unplugged it, plugged it back in and it powered up just fine. Apparently both units and the printer draw too much juice for them all to power up together.

Point is - I have no worries about my data's security since going to two units, one NAS backing up to another nightly. And with 3TB disks, you have a current max of 8.1TB (net after overhead) of volume on any one device. That is a lot of movies, for I don't think your critical files will be anywhere near that (mine are about 150GB).