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What is the usable disk space of a RAID 5 array of five 18 GB drives with one drive dedicated as a spare?
A. 18GB
B. 34GB
C. 54GB
D. 72GB
E. 90GB
Correct Answer: C
Explanation/Reference:
Explanation: The question states that you have 5 18GB drives, but one is dedicated as a spare. Therefore, you have the use of 4 drives which equals 72GB. When using RAID 5, parity data is written across the disks, using the equivalent of one disk’s space (18GB). Therefore, the total useable space is 72 – 18 = 54GB.
Reference: http://www.pc.ibm.com/us/infobrf/raidfin.html
Incorrect Answers
A:The total usable space is 54GB, not 18GB.
B:The total usable space is 54GB, not 34GB.
D: The equivalent of one drive is used for parity. Therefore, the total useable space is 72 – 18 = 54GB, not 72GB.
E: One drive is spare and the equivalent of one drive is used for parity. Therefore, the total useable space is 72 – 18 = 54GB, not 90GB.
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