Driven by the need for speed and server virtualization unified switching fabrics, Ethernet switch vendors are proposing to collapse three-tier data center architectures into two-tier ones.

Higher, non-blocking throughput from 10G Ethernet switches allows direct connection of server racks and top-of-rack switches to the core network, preventing the need for an aggregation layer. Also, in this system there is more application load on fewer servers due to the ability to decouple applications and operating systems from physical hardware.

The migration to a unified fabric that converges storage protocols onto Ethernet also requires a very low latency, lossless architecture that lends itself to a two-tier approach. Industry experts say that storage traffic cannot tolerate the buffering and latency of extra switch hops through a three-tier architecture that includes a layer of aggregation switching. This is where the 10G Ethernet comes into use.

“Over the next few years, the old switching equipment needs to be replaced with faster and more flexible switches,” says Robin Layland of Layland Consulting, an Adviser to IT users and vendors. “This time, speed needs to be coupled with lower latency, abandoning spanning tree and support for the new storage protocols. Networking in the data center must evolve to a unified switching fabric.”

Another factor that negates the three-tier approach to data center switching is server virtualization. Adding virtualization to blade or rack-mount servers means that the servers themselves take on the role of access switching in the network. Cost is also a key factor in driving two-tier architectures. Ten-gigabit Ethernet ports are inexpensive - about $500 or twice that of Gigabit Ethernet ports with 10 times the bandwidth. Virtualization means fewer servers to process more applications, which eliminates the need to acquire more servers.