Mirrored protection is a software availability function that protects data from being lost because of failure or because of damage to a disk-related component. Data is protected because the system keeps two copies of data on two separate disk units. When a disk-related component fails, the system may continue to operate without interruption by using the mirrored copy of the data until the failed component is repaired.
When you start mirrored protection or add disk units to a
disk pool that has mirrored protection, the system creates mirrored pairs
using disk units that have similar capacities. The overall goal is to protect
as many disk-related components as possible. To provide maximum hardware redundancy
and protection, the system attempts to pair disk units that are attached to
I/O buses, I/O adapter, I/O processors, buses, and expansion units. 
If a disk failure occurs, mirrored protection is intended to prevent data from being lost. Mirrored protection is a software function that uses duplicates of disk-related hardware components to keep your system available if one of the components fails. It can be used on any model of iSeries™ servers and is a part of the Licensed Internal Code.
Remote mirroring support allows you to have one mirrored unit within a mirrored pair at the local site, and the second mirrored unit at a remote site. For some systems, standard disk unit mirroring will remain the best choice; for others, remote disk unit mirroring provides important additional capabilities. You must evaluate the uses and needs of your system, consider the advantages and disadvantages of each type of mirroring support, and decide which is best for you.