Which of the following RAID arrays should be used to achieve a fault tolerant array with at least 1TB of storage space?

Five 250GB drives in RAID 0 provide 1.25TB of space, but RAID 0 offers no fault tolerance, as the failure of any single drive results in complete data loss.

Six 250GB drives in RAID 5 provide (N-1) * drive_size usable capacity, which is (6-1) * 250GB = 5 * 250GB = 1250GB or 1.25TB. RAID 5 is fault-tolerant as it can withstand the failure of a single drive without data loss, meeting both the storage and fault tolerance requirements.

Three 250GB drives in RAID 10 would require a minimum of four drives for a standard configuration and would provide only 500GB of usable space (2 x 250GB), which does not meet the 1TB requirement.

Six 250GB drives in RAID 1 (as mirrored pairs) would result in only 750GB of usable space (3 x 250GB), which is less than the required 1TB.