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: Show RAID Level Migration Example 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.

Show RAID Level Migration Example

Typically, a unit is reconfigured with the same or more storage capacity. Sometimes additional drives are added. The following table shows valid reconfigurations, some of which will require the addition of more drives.

Valid Migration Paths
	Destination
Source	R0	R1	R5	R6	R10	R50	Single	Spare
R0	Yes	No	Yes	Yes	Yes	Yes	No	No
R1	Yes	No	Yes	Yes	Yes	Yes	Yes	No
R5	Yes	No	Yes	Yes	Yes	Yes	No	No
R6	Yes	No	Yes	Yes	Yes	Yes	No	No
R10	Yes	No	Yes	Yes	Yes	Yes	No	No
R50	Yes	No	Yes	Yes	Yes	Yes	No	No
Single	Yes	Yes	Yes	Yes	Yes	Yes	No	No
Spare	No	No	No	No	No	No	No	No


	Note: Rapid RAID Recovery will be disabled on any unit that is migrated.


	Warning: If you are booted from a mirror (RAID 1 unit), never split it into 2 single (identical) drives. Once the unit is split, any pending writes cannot be written to the second drive. In addition, the file system on the drive will not be clean. Instead, shut down the system, replace one of the drives, and start the rebuild from 3BM.


	Note: You can only migrate a unit to a RAID level that has the same or more capacity as the existing one. A four-drive RAID 5 unit can migrate to a four-drive RAID 0, but a three-drive RAID 0 unit cannot migrate to a three-drive RAID 5, without adding another drive, due to the need for additional storage capacity for parity bits.

Related Topics: Changing An Existing Configuration by Migrating; Changing RAID Level; Expanding Unit Capacity; Informing the Operating System of Changed Configuration