RAID 6 (Striping with Dual Parity)

RAID 6 uses the striping technique in combination with dual parity to provide high fault tolerance. At least four physical disks are required to create a RAID 6 virtual disk/array, as shown in Figure 1. Data and parity information are striped across all physical disks, with RAID parity information requiring the equivalent of two physical disks, regardless of the number of physical disks.

Table 1 describes RAID 6 across a number of parameters.

Table 1  RAID 6

Parameter

Rating

Description

Read Performance

Read performance is good (due to striping) but write performance is comparatively lower because of the need to calculate and write parity information twice.

Write Performance

Fault Tolerance

The combination of striping and parity provides high fault tolerance. For virtual disks/arrays comprising of more than four physical disks, RAID 6 provides a more efficient use of physical disk space than RAID 1 (mirroring).

RAID 6 is similar to RAID 5, but dual parity provides the advantage of recovering data when up to two physical disks fail.

Efficient use of disk capacity

When the minimum four physical disks are used in a RAID 6 virtual disk/array, 50% of the combined disk capacity (two physical disks) is used for redundancy. The capacity efficiency increases as the number of physical disks increases (because only two physical disks are used for redundancy irrespective of the number of physical disks).

Automatic rebuild

Available

Minimum number of drives

 

4 

 

Figure 1 describes RAID 6.

Figure 1  RAID 6: Illustration

 

Figure 2 shows a Flash® demo of RAID 6.

Figure 2  RAID 6: Flash® Demo

Note: To view the Flash® demo for RAID 6, install the latest version of Adobe Flash Player at http://get.adobe.com/flashplayer/