I just read an interesting blog by Rob Aldrich on the advantages of "unified fabrics" when pursuing energy efficiency.
This story is more than just about gaining energy efficiency by reducing the amount of network hardware. Rather, it's all about using (and re-purposing) compute hardware more effectively.
A "unified fabric" is part of what we term "infrastructure orchestration" and "unified computing" - it is the abstraction of compute, I/O, storage and network infrastructure into a dynamically-configurable "fabric". In that way, servers and their associated infrastructure, can be logically-created and/or re-configured. It's a fantastic complement to virtualization. One way to think about it is that VMs provide a logical way to create or re-configure new software server stacks. In turn, infrastructure orchestration (the "fabric") is the way to provide a logical way to create or re-configure I/O, network and storage. So when you're moving VMs around (on purpose, or in response to an unplanned event) you can create compatible infrastructure on-the-fly.
What's the efficiency story here? The ability to re-purpose entire compute, network and storage systems on-the-fly, in response to compute demand. By using these resources more efficiently, data centers ultimately need fewer physical assets -- and those assests consume less power.
Going a step further, these assets can be re-purposed in response to energy efficiency triggers. Workloads can be moved a few feet in response to "hot spots", or to entirely different geographic locations based on power cost/availability.