I worry about my data too. I just built my first media server a couple of months ago and already have over 275 blu-ray and another 40ish DVD rips from our movie collection. I also am using it as a backup for our photos and videos. I did, however, set up an external drive for the backup drive of those photos and videos so that if something happens at the house (and we are able to) I could grab the external drive as I am running out the door. I also have taken yearly sets of photos and backed them up on to DVD (and recently on to dual layer blu-ray discs) and send them off every Christmas to my in-laws who live out of state. That is my offsite backup for them.
But that still leaves me with the movie rips. It would take a LOT of time to re-rip things in the case of a disaster. I am using FlexRAID (another software RAID5 solution) and should have similar recovery options based off of what you are saying about UnRAID. I too looked at the cloud, but came to the same conclusions about backup time, my monthly cap, issues with shipping drives initially, plus just the understanding that if a big failure happened and I needed to recover 2 drives (since I can recover locally from a single drive failure), that would be 6TB of data to download (two 3TB drives). So cloud storage doesn't work for that type of situation. Heck, with my monthly internet cap at 250GB, I can't even come up with an over-the-internet backup of too many rips to say a backup server at my in-laws. I still need to use the internet for other things. Sure, maybe when I get done with my last approx 30 blu-ray rips, things will slow down, but I have been trying to come up with a solution myself.
My server has six 3TB drives and I don't have the amount of used storage, but it is still a LOT of data used. Just the drives alone would run me about $600 if I get them on sale. Sure the backup wouldn't need much horsepower, but still requires a decent mobo for that number of sata ports, and the usual case, power supply, etc. I don't need fast, but I like quality.
So maybe in spring or something after we get past some recent and upcoming significant expenses, but even still, like you say, it isn't off-site or anything, so a fire, flood, or whatever would still not save either machine. At that point, wouldn't it be better to have a drive sitting either unused in a box, or online as a "hot" spare to do a rebuild right at the time of failure? It would take time to rebuild that drive using the parity data, but would be faster than having to wait for a drive to be ordered and shipped. You still have the same level of catastrophic failure protection from a drive failure point of view, and are no worse off in the case of fire/flood, but for less money.
Of course, like I mentioned, I am out of sata ports to make something a spare, but maybe I should at least buy ONE drive as a disaster replacement for $100 until something different can be done later.
Bet you didn't realize that you would get such a lengthy response to your post about data backup.