Avago Technologies 3ware 9650SE-12ML (Channel) - Manual (Page 142)

Configuring Units
130 3ware SAS/SATA RAID Software User Guide, Version 9.5.1
Changing RAID Level
You can use migrate to change the RAID level of an existing unit while the
unit is online, without experiencing any data loss. When you change a RAID
level, you may also add one or more drives to the unit. You can also migrate to
change the unit's stripe size. For example, a four-drive RAID 5 with a 64KB
stripe size can be migrated to a four-drive RAID 5 with 256KB stripe size.
The steps below describe how to change a RAID level in 3DM 2.
To change the RAID level of a unit
1 In 3DM 2, choose Management > Maintenance .
2 In the Unit Maintenance table on the Maintenance Page, select the unit for
which you wish to change the RAID level, by checking the box next to
the Unit ID.
3 Click the Migrate Unit button.
The Migrate dialog box appears.
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.
Note: Once migration starts, the unit stays in the migrating state until the migration
process is complete. The migration process cannot be aborted, and must be
allowed to finish before a rebuild or verify to the unit is permitted.
Warning: It is important that you allow migration to complete before removing any
drives that are involved in the migration. Removing drives from the unit during
migration may cause the migration process to stop, and can jeopardize the safety of
your data.
The unit to be migrated must be in a normal state (not degraded,
initializing, or rebuilding) before starting the migration.