Starting device parity protection

Often, you start device parity protection when you attach a new disk subsystem to your system.

Ideally, you should start device parity protection before you add the disk units to the software disk configuration. When you start device parity protection for disk units that are already being used, the system must move data off of the disk units to other disk units in the auxiliary storage pool (ASP) in order to make space available for the parity data. The performance for starting device parity protection is much better if the system does not have to move data.

When you start device parity protection, the system does validity checking and moves data from the required units, if necessary. For some types of disk units, you or your service representative must perform tasks with the disk subsystem when you start device parity protection.

• The configuration must be complete and no disk units can be missing in any ASPs that contain disk units that are to have device parity protection. This is because the system must move data off the disks that are to be protected to make room for parity information.
• The disk units that will become device-parity protected cannot be in an ASP that has mirrored protection active. If the disk units are in an ASP that has mirrored protection, you must stop mirrored protection before starting device parity protection.
• When you start device parity protection, you reduce the capacity of some of the disk units in the subsystem. The system must have sufficient storage in each affected ASP to make room for redundant parity data.