vSAN

When you study how vSAN works then you will read about how objects are backed by one or more components. This is dependent on the fault tolerance level and what you would also read is that a tie-breaker witness will be created. This is to make sure that when a network partition occurs, servers in a network partition can decide whether or not they together hold more than 50% of the necessary components and/or witnesses. 

The Distributed Resource Scheduler (DRS) allows vSphere Administrators to use rules to enforce virtual machine placement on cluster nodes. An example of such a rule is in the image below with a rule to reparate two domain controllers so that they won't run on the same vSphere host.