“ You should distinguish between availability (the data is there when you need it, even if a drive happens to fail at that point) and backup (you can restore from some other place, if/when you screw up).
RAID isn't backup, it gives you availability in some situations. I'd keep data on two Drobo, and syncronize it somehow.
Then, if you delete a file (for example) you can restore it from the backup. As far as I know, Drobo doesn't save you from yourself. ”