Cisco's vision is one in which big companies off-load an increasing number of server tasks to network switches, with servers ultimately becoming little more than virtual machines inside a switch. The Nexus doesn't deliver that, but it makes a start, aiming to virtualize the network interface cards, host bus adapters, and cables that connect servers to networks and remote storage. At present, those require dedicated local area networks and storage area networks, with each using a separate network interface card and host bus adapter for every virtual server. The Nexus aims to consolidate them all into one (or two, for redundancy), with virtual servers connecting through virtual NICs.
Cisco's interest in expanding the network's scope is obvious--the Catalyst 6500 platform alone has generated more than $20 billion in revenue over its lifetime. But Cisco isn't the only one moving toward virtual I/O. Brocade last week introduced the DCX Backbone, a switch that aims to do much the same as Cisco's Nexus: consolidate SAN and LAN into a single network, and virtualize the NICs that connect them to virtual servers. But the two companies take a different approach at the physical layer, a function of their different roots.
As a router company, Cisco bases its networks on Ethernet: Virtual servers may see a virtual Fibre Channel SAN, but really they're using an Ethernet cable that's shared with other network traffic. The Nexus can still use Fibre Channel, but only for connections to legacy storage targets such as disk drives, and only because disks have a slower replacement cycle than servers, so older systems stay in use longer. Conversely, storage company Brocade uses Fibre Channel for the physical connection to servers, running virtual Ethernet to virtual servers. Brocade expects that it eventually will migrate to Ethernet, too, but that right now Fibre Channel is more reliable.