Which method of fault tolerance is least expensive per MB of storage disk duplexing or disk striping with parity?

has to be raid 5. raid5 with the parity will consume about 1/3 of the disk space but will give just about the highest level of fault tolerance.

raid0 - disk striping - will give you the full disk space but no fault tolerance

raid1 - disk splitting/ duplexing - will give you full redundancy but will cost 50% of your disk space

raid5 - parity - will do block-level striping with parity data , disk space cost about 30%, redundant