With the release of vSphere 6 update 1, and Virtual SAN 6.1, VMware is expanding the capabilities of Virtual SAN as a platform and is introducing higher levels of enterprise availability and data protection of the solution.
Virtual SAN 6.1 introduces the new feature Stretched Cluster. Virtual SAN Stretched Clusters provides customers with the ability to deploy a single Virtual SAN cluster across multiple data center.
Some of the critical aspects of Virtual SAN refocused around the mitigation of interruptions in operations ensuring that data is never lost, in Virtual SAN 6.1 Stretched Cluster furthers that concept by enabling the ability for no interruption in operations even in the event of a complete site failure. Virtual SAN Stretched Cluster is a specific configuration implemented in environments where disaster/downtime avoidance is a key requirement
Source: http://www.yellow-bricks.com/