Network Subsystem Reliability
By definition a network server has to be attached to a network. This attachment is made possible by a network interface card (NIC) installed in the network server. If the NIC fails, the network server can no longer communicate with other computers on the network. Even though the network server is still fully operational, this inability to communicate on the network makes it useless. Many network servers (through both hardware and software) support redundant NICs. Redundant NICs can be implemented in two different ways: fail-over and load balancing. In the NIC fail-over implementation, one NIC is used to communicate to the network and the other NIC is held in reserve until the primary NIC fails, at which time it is automatically activated. In the NIC load-balancing implementation, both NICs are operational (thus improving the capability of the network server to communicate on the network). The failure of a single NIC, in this implementation, only decreases the capability of the network server to communicate on the network. A PCI expansion bus with hot-swap capability in the network server allows for replacement of a failed NIC without having to shut down the network server.