Which of the following provides the LEAST availability?
A. RAID 0
B. RAID 1
C. RAID 3
D. RAID 5
Correct Answer: A
Section: Compliance and Operational Security
RAID, or redundant array of independent disks (RAID). RAID allows your existing servers to have more than one hard drive so that if the main hard drive fails, the system keeps functioning. RAID 0 is disk striping. It uses multiple drives and maps them together as a single physical drive. This is done primarily for performance, not for fault tolerance. If any drive in a RAID 0 array fails, the entire logical drive becomes unusable.
B: RAID 1 is disk mirroring. Disk mirroring provides 100 percent redundancy because everything is stored on two disks. If one disk fails, another disk continues to operate. The failed disk can be replaced, and the RAID 1 array can be regenerated. This system offers the advantage of 100 percent data redundancy at the expense of doubling the storage requirements. Each drive keeps an exact copy of all information, which reduces the effective storage capability to 50 percent of the overall rated storage.
C: RAID 3 is disk striping with a parity disk. RAID 3 arrays implement fault tolerance by using striping (RAID 0) in conjunction with a separate disk that stores parity information. Parity information is a value based on the value of the data stored in each disk location. This system ensures that the data can be recovered in the event of a failure. The process of generating parity information uses the arithmetic value of the data binary. This process allows any single disk in the array to fail while the system continues to operate.
D: RAID 5 is disk striping with parity, and it is one of the most common forms of RAID in use today. It operates similarly to disk striping, as in RAID 0. The parity information is spread across all of the disks in the array instead of being limited to a single disk, as in RAID 3. Most implementations require a minimum of three disks and support a maximum of 32.
Dulaney, Emmett and Chuck Eastton, CompTIA Security+ Study Guide, 6th Edition, Sybex, Indianapolis, 2014, pp. 34-35, 234