Today VMware have annouced the support for ‘stretched storage cluster’ and have produced a white paper to this effect.
The purpose behind a ‘stetched storage cluster’ is to have two different geographical sites which reside on the same subnet (stretched VLAN) to enable routine tasks as high availability, vMotion and Storage vMotion to take place. It is not intended to replace VMware Site Recovery Manager.
Essentially, you need to have an array which has the ability to perform reads to and writes to both locations at the same time. The white paper mentions latency values up to 5ms, however, my experience with synchronous SAN based replication is that we encountered performance hits with latency above 2ms.
The white paper can be found at VMware vSphere Metro Stroage Cluster