In vSAN virtual machines in your inventory have an association with the objects on the vSAN datastore. If you would remove a virtual machine from the inventory but not from disk then the objects on disk will still consume disk space but you will not able to see the direct link with the virtual machine that was previously in your inventory. Such objects on your vSAN datastore are known as unassociated objects.
The performance statistics in vSAN are stored in a database object on the vSAN Datastore in a vSAN enabled cluster. Information about the object can be found in the vSphere Client under the Services tab of the vSAN Cluster Configuration. The image below shows the objects's status and that it's protected under the vSAN Default Storage Policy.
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.
