# Understanding RAID level-5EE

Note: This feature is not supported on all ServeRAID controllers.

RAID level-5EE is similar to RAID level-5E but with a more efficient distributed spare and faster rebuild times. Like RAID level-5E, this RAID level stripes data and parity across all of the drives in the array.

RAID level-5EE offers both data protection and increased throughput. When an array is assigned RAID level-5EE, the capacity of the logical drive is reduced by the capacity of two physical drives in the array: one for parity and one for the spare.

The spare drive is part of the RAID level-5EE array. However, unlike RAID level-5E, which uses contiguous free space for the spare, a RAID level-5EE spare is interleaved with the parity blocks, as shown in the following example. This allows data to be reconstructed more quickly if a physical drive in the array fails. With such a configuration, you cannot share the spare drive with other arrays. If you want a spare drive for any other array, you must have another spare drive for those arrays.

RAID level-5EE requires a minimum of four drives and, depending upon the level of firmware and the stripe-unit size, supports a maximum of 8 or 16 drives. RAID level-5EE is also firmware-specific.

Note: For RAID level-5EE, you can have only one logical drive in an array.

The following illustration is an example of a RAID level-5EE logical drive.

## RAID level-5EE example

Start with four physical drives. |
Create an array using all four physical drives. |
Then create a logical drive within the array. |
The data is striped across the drives, creating blocks in the logical drive. The storage of the data parity (denoted by *) is striped, and it shifts from drive to drive as it does in RAID level-5E. The spare drive (denoted by S) is interleaved with the parity blocks, and it also shifts from drive to drive. |
If a physical drive fails in the array, the data from the failed drive is reconstructed. The array undergoes compaction, and the distributed spare drive becomes part of the array. The logical drive remains RAID level-5EE. When you replace the failed drive, the data for the logical drive undergoes expansion and returns to the original striping scheme. |

If you use a RAID level-5EE logical drive in a failover or cluster configuration, the RAID level-5EE logical drive will not failover while undergoing compaction or expansion.

RAID level-5EE offers the following advantages and disadvantages.

Advantages | Disadvantages
--- | ---
100% data protection Offers more physical drive storage capacity than RAID level-1 or level-1E Higher performance than RAID level-5 Faster rebuild than RAID level-5E | Lower performance than RAID level-1 and level-1E Supports only one logical drive per array Cannot share a hot-spare drive with other arrays Not supported on all ServeRAID controllers

Note: The Configuration wizard does not default to RAID level-5EE. If you have four physical drives, Express configuration defaults to RAID level-5 with a hot-spare drive.

## 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-x0

Glossary | Contents

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