Typically, data centers are connected via routed connections between core switches at each data center. There are different topologies of course, but this is a stypical scenario.
Spanning layer 2 across data centers has its challenges with regard to loop mitigation and other l2 considerations. The advantage of having l2 spanned across data centers is VM mobility, for one...Im sure there are other advantages...
To this end, Cisco has introduced OTV (Overlay Transport Virtualization), which basically spanns the forwarding plane across data centers, while localizing the control plane to mitigate layer 2 challenges.
Moreover, Cisco has introduced Fabric Path, which leverages a routing protocol (I think IS-IS) to create a switched domain that utilizes 100% of the cross sectional bandwidth in a non-blocking architecture. So there is no need for STP or worries about having to limit the diameter of the L2 domain. This is Ciscos equivalent to TRILL.
Can anyone offer their thoughts, perceptions, predictions, regarding data center connectivity innovations other than the ones I mentioned. I am not looking for a fill-in-the-blank answer; Im looking more for someone who has thoughts about these topics.