AMCC 720-0138-00 manual Changing An Existing Configuration, RAID Level Migration RLM Overview

Chapter 5. Configuring Units

Changing An Existing Configuration

You can convert one RAID configuration into another while the unit is online. This process is known as RAID Level Migration (RLM).

You can use RAID Level Migration to make two main types of configuration changes:

•RAID Level (for example, a RAID 1 to a RAID 5)

•Unit Capacity Expansion (for example, adding a 4th drive to a 3-drive RAID 5)

You can also use RLM to change the stripe size of a unit.

Note: A unit being migrated can still be used (I/O still continues), however the performance will be affected while the migrating task is active. You can control how much effect this has on performance by setting the background task rate. For more information, see “Setting Background Task Rate” on page 112.

This section includes the following topics about changing existing configurations:

•RAID Level Migration (RLM) Overview

•Changing RAID Level

•Expanding Unit Capacity

•Informing the Operating System of Changed Configuration

If you want to change the policy settings for an existing unit, there is no need to change the configuration. See “Setting Unit Policies” on page 44.

RAID Level Migration (RLM) Overview

RAID level migration is the process of converting one RAID configuration to another. When you migrate a unit to a different configuration, the user data on it is redistributed to the format of the new configuration. This data redistribution process is a background task, similar to the rebuild or verify processes.

Figure 22 shows an example of how data is reconfigured during a migration. In this example, the migration is from a 3-drive RAID 0 to a 4-drive RAID 5, with both having the same stripe size. As can be seen, every piece of user data is moved from its original physical location.

50 3ware Serial ATA RAID Controller User Guide for the Power Mac G5