Of the following options, which one is the only RAID level that uses disk mirroring?

A.
RAID-0

B.
RAID-5

C.
RAID-3

D.
RAID-1

Explanation:
RAID 1 is the most common form of RAID at the moment and is often used in disk mirroring and disk duplexing.
Incorrect Answers:
A: RAID Level 0 (RAID 0) is the no-fault-tolerance process of using 64KB block storage areas in a striped set.
B: RAID-5 is a fault-tolerant volume with data and parity striped intermittently across three or more physical disks.
C: RAID 3 is disk striping with parity, with data being moved at the bit level rather than the block level.
Reference:
James G. Jones and Craig Landes, A+ Exam Cram 2 (2nd Edition), QUE Publishing, Indianapolis, 2003, pp. 731 and 732.