Which of the following is often implemented by a one-for-one disk to disk ratio?

A.
RAID Level 1

B.
RAID Level 0

C.
RAID Level 2

D.
RAID Level 5

Explanation:
RAID Level 1 is commonly called mirroring. It mirrors the data from one disk or set of disks by duplicating thedata onto another disk or set of disks. This is often implemented by a one-for-one disk to disk ratio: Each drive
is mirrored to an equal drive partner that is continually being updated with current data. If one drive fails, the
system automatically gets the data from the other drive. The main issue with this level of RAID is that the onefor-one ratio is very expensive — resulting in the highest cost per megabyte of data capacity. This level
effectively doubles the amount of hard drives you need, therefore it is usually best for smaller capacity systems.
Incorrect Answers:
B: RAID level 0 is not implemented by a one-for-one disk to disk ratio.
C: RAID level 2 is not implemented by a one-for-one disk to disk ratio.
D: RAID level 5 is not implemented by a one-for-one disk to disk ratio.

Krutz, Ronald L. and Russell Dean Vines, The CISSP Prep Guide: Mastering the CISSP and ISSEP Exams,
2nd Edition, Wiley Publishing, Indianapolis, 2004, p. 144