ZFS? That's a very odd way of spelling
ReFS 
My personal backup strategy was tested last year when a leaky boiler dripped onto my home server, frying the power supply, and ruining a USB HDD that was sitting on top
Luckily a change of PSU fixed the server and all the disks inside are fine, but the USB HDD was toast.
At that point I was technically down to two copies of my data: one cached on my laptop (actually incomplete as it has a small SSD so not everything is cached), and one on the other backup HDD. Bit too close for comfort...