# Understanding RAID level-1

RAID level-1 uses data mirroring. Two physical drives are combined into an array, and data is striped across the array. The first half of a stripe is the original data; the second half of a stripe is a mirror (that is, a copy) of the data, but it is written to the other drive in the RAID level-1 array.

RAID level-1 provides data redundancy and high levels of performance, but the storage capacity is diminished. Because the data is mirrored, the capacity of the logical drive when assigned RAID level-1 is 50% of the array capacity.

RAID level-1 requires two physical drives.

The following illustration shows an example of a RAID level-1 logical drive.

## RAID level-1 example

Start with two physical drives. |
Create an array using the two physical drives. |
Then create a logical drive within that array. |
The data is striped across the drives, creating blocks. Notice that the data on the drive on the right is a copy of the data on the drive on the left. |

With RAID level-1, if one of the physical drives fails, the controller switches read and write requests to the remaining functional drive in the RAID level-1 array.

RAID level-1 offers the following advantages and disadvantages.

Advantages | Disadvantages
--- | ---
100% data redundancy High performance | Allows only 50% of the physical drive storage capacity to be used

## More information

- Understanding RAID technology
- Understanding stripe-unit size
- Selecting a RAID level
- RAID level-0
- RAID level-1 Enhanced
- RAID level-5
- RAID level-5 Enhanced
- RAID level-5EE
- RAID level-6
- RAID level-x0
- RAID volumes
- Software and hardware support of RAID levels

Glossary | Contents

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