For years, I have used a 2nd external HDD equal or larger than the internal. I back up the entire drive, and I mean everything. I only turn on that drive for back-ups and when disconnected from the internet. Yes, I am paranoid, but am I paranoid enough?

If the worst happens, fire, crash, destructive virus, I have a complete back up of everything. I always said that, in case of fire, I'd grab the external drive and run. While I have been fortunate in that respect it has saved my bacon on a couple of other occasions.