AHCI and RAID on HP Compaq dc7800

Table 4 RAID 5 with 3 hard drives (Parity)

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 compro-

mised.

To better illustrate the concept of RAID 5 (parity based RAID), the following figure shows how a sequence

of data “ABCD...” is stored in a RAID 5. In this example, each letter represents a segment or strip. The fig-

ure shows how 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

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