# Understanding RAID level-6

RAID level-6 is similar to RAID level-5 but with two sets of parity information instead of one. RAID level-6 stripes blocks of data and parity across all drives in the array like RAID level-5, but adds a second set of parity information for each block of data.

When you assign RAID level-6 to an array, the capacity of the array is reduced for data-parity storage (the exact amount depends on the size of the drives in the array). The second set of parity information is added to improve fault tolerance. RAID level-6 can handle two simultaneous drive failures, where other single RAID levels can handle, at most, only one.

RAID level-6 requires a minimum of four drives and supports a maximum of 16 drives. The maximum stripe-unit size depends on the number of drives in the array.

The following illustration is an example of a RAID level-6 logical drive.

## RAID level-6 example

Start with six physical drives. |
Create a logical drive using four physical drives, leaving two for hot spare drives. |
The data is striped across the drives, creating blocks in the logical drive. The storage of the data parity (denoted by * and **) is striped, and it shifts from drive to drive as it does in RAID level-5. |
If a physical drive fails in the array, the logical drive is degraded but remains fault tolerant. |
If a second physical drive fails in the array, the data from the failed drives are reconstructed onto the hot-spare drives, and the data for the logical drive return to the original striping scheme. |

RAID level-6 offers the following advantages and disadvantages.

Advantages | Disadvantages
--- | ---
100% data protection Extremely high data fault tolerance Can sustain two simultaneous drive failures Good solution for mission critical applications | Lower performance than RAID level-5 because of two parity drives Not supported on all controllers

## More information

- Understanding RAID technology
- Understanding stripe-unit size
- Selecting a RAID level
- RAID level-0
- RAID level-1
- RAID level-1 Enhanced
- RAID level-5
- RAID level-5E Enhanced
- RAID level-x0
- RAID volumes

Glossary | Contents

x-1111-SRM-00-12-EN