Mirroring stores multiple copies of data on a system. When properly applied, mirroring provides continuous availability of data and protection against data loss due to physical media failure. Mirroring improves the chance of data recovery in the event of a system crash or the failure of a disk or other hardware.
In some cases, you can also use mirroring to improve I/O performance. Unlike striping, the performance gain depends on the ratio of reads to writes in the disk accesses. If the system workload is primarily write-intensive (for example, greater than 30 percent writes), mirroring can result in reduced performance.