Determine the disk units that are needed

A mirrored disk pool requires twice as much storage as a disk pool that is not mirrored because the system keeps two copies of all the data in the disk pool. Also, mirrored protection requires an even number of disk units of the same capacity so that disk units can be made into mirrored pairs. On an existing system, it is not necessary to add the same types of disk units already attached to provide the required additional storage capacity. Any new disk units may be added as long as sufficient total storage capacity and an even number of storage units of each size are present. The system assigns mirrored pairs and automatically move the data as necessary. If a disk pool does not contain sufficient storage capacity, or if storage units cannot be paired, mirror protection cannot be started for that disk pool.

The process of determining the disk units that are needed for mirrored protection is similar for existing or new systems. You and your IBM^® marketing representative should do the following:

1. Plan for storage capacity.
2. Plan a target percent of storage used for the disk pool (how full the disk pool can be).
3. Plan the number and type of disk units needed to provide the storage that is required. For an existing disk pool, you can plan a different type and model of disk unit to provide the required storage. You must ensure an even number of each type of disk unit and model.
4. Plan for disk pools.
5. Plan total storage capacity.

• Plan for storage capacity
  
• Plan for spare disk units
  
• Plan for total storage capacity