# Understanding RAID level-x0

Note: RAID level-x0 is available only on IBM ServeRAID-4 Ultra160 SCSI controllers.

RAID level-x0 refers to RAID level-00, 10, 1E0, and 50. RAID level-x0 uses an array of arrays, or a spanned array. The operating system uses the spanned array logical drive in the same way as a regular array logical drive.

RAID level-x0 allows more physical drives in an array. The benefits of doing so are larger logical drives, increased performance, and increased reliability. RAID level-0, 1E, 5, and 5E cannot use more than 16 physical drives in an array; however, RAID level-1E0 and 50 support 60 drives.

RAID level-x0 requires a minimum of two drives and supports a maximum of 60 drives.

The following illustration is an example of a RAID level-10 logical drive.

## RAID level-10 example

Start with six physical drives. |
Create three arrays (labeled A, B, and C), each array using two physical drives. |
Then create a spanned array (labeled as *) that spans the three arrays. |
A sub-logical drive is created within each array (A, B, and C). Then the data is striped across the physical drives in the array, creating blocks. Notice that, in each array, the data on the drive on the right is a copy of the data on the drive on the left. This is because the sub-logical drives (A, B, and C) are RAID level-1 in a RAID level-10 implementation (see the following table). |
Then create a logical drive within the spanned array (*). The data is striped across this logical drive, creating blocks (1-12). Notice that none of these blocks are redundant. This is because the logical drive is RAID level-0 in a RAID level-x0 implementation (see the following table). |

RAID level | Sub-logical drive | Spanned array logical drive
--- | --- | ---
00 | RAID level-0 | RAID level-0
10 | RAID level-1 | RAID level-0
1E0 | RAID level-1E | RAID level-0
50 | RAID level-5 | RAID level-0

With RAID level-10, 1E0, and 50, if one of the physical drives fails in a sub-logical drive, the ServeRAID controller switches read and write requests to the remaining functional drives in the sub-logical drive. With RAID level-00, a physical drive failure within the sub-logical drive results in loss of data.

RAID level-x0 offers the following advantages and disadvantages.

Advantages | Disadvantages
--- | ---
Supports up to 60 physical drives 100% data redundancy (except for RAID level-00) | Available only on the IBM ServeRAID-4 Ultra160 SCSI controllers No data redundancy for RAID level-00

## 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-5 Enhanced

Glossary | Index | Contents

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