Mirrored protection increases the availability of a server by duplicating different disk-related hardware components, such as a disk controller, a disk I/O processor, or a bus. The server can remain available after a failure, and service for the failed hardware components can be scheduled at a convenient time.
Different levels of mirrored protection provide different levels of server availability. For example, if only the disk units on a server are mirrored, all disk units have disk unit-level protection, so the server is protected against the failure of a single disk unit. In this situation, if a controller, I/O processor, or bus failure occurs, the server cannot run until the failing part is repaired or replaced. All mirrored units on the server must have identical disk unit-level protection and reside in the same ASP. The units in an ASP are automatically paired by the server when mirrored protection is started.