System Mirroring uses special order hardware that will take over the processing in case of a system failure. System Mirroring is for systems that can not have any down time. It is a computer that is a copy of another computer and stands by and waits to take over in the event a system failure. If the first computer fails, the second computer will automatically take over the processing, so that there is virtually no down time on the server.
This solution works very well with virtualization such as VMWare, Hyper-V, or XEN-OS.