We have a Xserve storage running raid, plugged into the Mac server.
The Xserve storage has two raid controllers both of which handle 2Gb, these two links are then running to the Mac server, and a single 1Gb ethernet to the switch and LAN.
That doesn't come to 5Gb/s. That's just 1Gb/s.
Those are storage controllers, not RAID controllers. They have RAID, but they aren't a "RAID controller" in the normal sense. They are small servers. 2Gb/s is the Fibre Channel speed.