# Understanding stripe-unit size

With RAID technology, data is striped across an array of physical drives. This data-distribution scheme complements the way the operating system requests data.

The granularity at which data is stored on one drive of the array before subsequent data is stored on the next drive of the array is called the stripe-unit size.

You can set the stripe-unit size to 8 KB, 16 KB, 32 KB, or 64 KB. You can maximize the performance of your ServeRAID controller by setting the stripe-unit size to a value that is close to the size of the system I/O requests. For example, performance in transaction-based environments, which typically involve large blocks of data, might be optimal when the stripe-unit size is set to 32 KB or 64 KB. However, performance in file and print environments, which typically involve multiple small blocks of data, might be optimal when the stripe-unit size is set to 8 KB or 16 KB.

The collection of stripe units, from the first drive of the array to the last drive of the array, is called a stripe.

Attention: After you configure an array and store data on the logical drives, you cannot change the stripe-unit size without destroying data in the logical drives.

You can set the stripe-unit size to 8 KB, 16 KB, 32 KB, or 64 KB. The default setting is 8 KB data bytes.

- When the stripe-unit size is 8 KB or 16 KB, the maximum number of physical drives in an array is 16.

- If you have a ServeRAID-3H or ServeRAID-3HB controller using ServeRAID firmware (version 4.0, or later) and the stripe-unit size is 32 KB or 64 KB, the maximum number of physical drives in an array is 16. Otherwise, when the stripe-unit size is 32 KB or 64 KB, the maximum number of physical drives in an array is 8.

- If you have a ServeRAID-4 controller and the stripe-unit size is set to 32 KB or 64 KB, the maximum number of physical drives in an array is 16.

## More information

- Changing the stripe-unit size (action)
- Application environment groups reference

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