How do Redundant RAID Controllers work ? What happens if one fails?

The ActiveRAID is a true Active/Active storage system. The RAID controllers work
independently but offer full redundancy in the unlikely event of a controller failure. If either controller
fails, the surviving controller takes over seamlessly and no data loss occurs. It should be noted that
the ActiveRAID offers 4 x 4 Gb FC with two ports per controller. The load in normal mode is
balanced across the controllers and all 4 ports in order to deliver the highest throughput. If a controller
fails, the system will continue to deliver data, but only through the surviving 2 ports thus dropping the
overall performance of the system. Once a good RAID controller is swapped in, the system rebalances
automatically and returns to normal throughput.