RAID
RAID (Redundant Array of Independent Disks) combines multiple disks into one logical disk through hardware controllers (good) or software (usually bad).
SnapRAID is an interesting tool that I have yet to test. From their description, its use case is for multi terabyte partial disk backup, in case you do not have enough mirror disks for a full backup. It uses a changeable amount of parity drives based on your protection needs (data salvageable if 1 disk goes down, or 2, …)