HP 8200 tower manual RAID 5 with three hard drives, First disk Second disk Third disk

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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