Because mirrored protection is configured by disk pool, you can mirror one, some, or all disk pools on the system. By default, every system has a system disk pool. It is not necessary to create user disk pools in order to use mirrored protection. Although mirrored protection is configured by disk pool, all disk pools must be mirrored to provide for maximum system availability. If a disk unit fails in a disk pool that is not mirrored, the system cannot be used until the disk unit is repaired or replaced.
The start mirrored pairing algorithm automatically selects a mirrored configuration that provides the maximum protection at the bus, I/O (input/output) processor, or I/O adapter for the hardware configuration of the system. When storage units of a mirrored pair are on separate buses, they have maximum independence or protection. Because they do not share any resource at the bus, I/O processor, or I/O adapter levels, a failure in one of these hardware components allows the other mirrored unit to continue operating.
Any data that is written to a unit that is mirrored is written to both storage units of the mirrored pair. When data is read from a unit that is mirrored, the read operation can be from either storage unit of the mirrored pair. It is transparent to the user which mirrored unit the data is being read from. A user is not aware of the existence of two physical copies of the data.
If one storage unit of a mirrored pair fails, the system suspends mirrored protection to the failed mirrored unit. The system continues to operate using the remaining mirrored unit. The failing mirrored unit can be physically repaired or replaced.
After the failed mirrored unit is repaired or replaced, the system synchronizes the mirrored pair by copying current data from the storage unit that has remained operational to the other storage unit. During synchronization, the mirrored unit to which the information is being copied is in the resuming state. Synchronization does not require a dedicated system and runs concurrently with other jobs on the system. System performance is affected during synchronization. When synchronization is complete, the mirrored unit becomes active.
For details on storage on your server, see Disk storage concepts.