RAID 5 with three hard drives

RAID 5 has been used in servers for many years and is one of the most common types of RAID. RAID 5 uses striping with parity data in distributed blocks across all member disks. Therefore, the mass storage controller can simultaneously write new information to two hard drives and parity information to the third hard drive, so if one hard drive fails, the RAID controller can rebuild all the information after the volume degradation occurred. Hence, RAID 5 with three hard drives has similar performance to RAID 0 with two hard drives, and the reliability of RAID 1 with a minimum of three hard drives.

Table 5: RAID 5 with three hard drives (parity)

First disk

Second disk

Third disk

 

 

 

Data Segment 1

Data Segment 2

Parity for 1 and 2

 

 

 

Data Segment 3

Parity for 3 and 4

Data Segment 4

 

 

 

Parity for 5 and 6

Data Segment 5

Data Segment 6

 

 

 

Data Segment 7

Data Segment 8

Parity for 7 and 8

 

 

 

Data Segment 9

Parity for 9 and 10

Data Segment 10

 

 

 

Parity for 11 and 12

Data Segment 11

Data Segment 12

 

 

 

Data Segment 13

Data Segment 14

Parity for 13 and 14

 

 

 

Data Segment 15

Parity for 15 and 16

Data Segment 16

 

 

 

Parity for 17 and 18

Data Segment 17

Data Segment 18

 

 

 

In the previous table, each “Data Segment x” represents a strip. A stripe is made with strip “Data Segment x”, “Data Segment y” and strip “Parity for x and y.” Notice that the strip “Parity for x and y” is used to store the required information to recreate the data if any one of the RAID volume members is compromised.

To better illustrate the concept of RAID 5 (parity-based RAID), Figure 4 shows how a sequence of data “ABCD...” is stored in a RAID 5. In this example, each letter represents a segment or strip. The various pieces of the information go to different hard drives, hence if any one member of the RAID 5 fails, the information from all members is not lost.

Figure 4: RAID 5 with three hard drives

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