I agree that an OS on the 10 isn't the best way to use it, and stuffing an SSD (if a fast OS/applications disk is desired and within budget), can be placed in the empty optical bay. No risk of the ICH throttling either.
You could get another pair of 2TB disks and JBOD them in an external enclosure (or stripe, though for backup, I prefer JBOD, as if you lose a disk, you don't lose all the data, just what was on the failed disk). And you should be able to restore that off of the primary data location (odds of a dual primary and backup failure are possible, but not all that likely - usually due to a power problem of some kind when it does). Cheap to do as well (inexpensive enclosure, perhaps Port Multiplier based, and an eSATA card).
Just a thought anyway...