After fielding a number of questions around this topic recently, its come to my attention that there is a misunderstanding on how to implement the vSphere Storage Appliance (VSA) for certain ROBO solutions. The requirement around the tie-breaker code (VSA Cluster Service) is either misunderstood or misinterpreted when it comes to 2 node VSA deployments at remote office/branch office (ROBO) sites.
Let’s be clear about it now – the VSA needs 3 votes in order to function correctly as a cluster. In a 3 node VSA deployment, this is not an issue since each node gets a vote. In a 2 node VSA deployment, the third vote is handled by the VSA Cluster Service aka the tie-breaker code.
Now, in standard (non ROBO) 2 node VSA deployments where the vCenter is located in the same datacenter as the VSA, the VSA Cluster Service can exist on the vCenter server. During VSA installation, you simply provide the IP address of the vCenter server for the VSA Cluster Service.
However, in ROBO deployments, things are a little different. In these deployments, the vCenter server is typically located at a central office, and the 2 node VSA is deployed at a remote office. The third vote (tie-breaker code) must also be located at the remote office/branch office. To cater for this, we allow the VSA Cluster Service to be decoupled from vCenter and installed in a VM. The VM can be running on a non-VSA ESXi host or Workstation at the branch office. We cannot have it run on the ESXi hosts involved in the VSA cluster because if we lost the host on which the tie-breaker VM was running, we lose 2 votes, and thus the cluster quorum. So it must exist outside of the VSA.
--> Please read the rest on the blog : http://blogs.vmware.com/vsphere/2012/11/considering-vsa-for-robo-please-read-this.html