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.
It's possible to edit the policy assignment which allows you to adjust the fault tolerance level for the DB Stats Object.
In this article I would like to explain how to verify the physical placement of the Performance DB Stats Object. First in the vSphere Client and next in Ruby vSphere Console.
On the cluster object access the Monitor-tab and select Virtual Objects. The Performance management object will usually be almost at the bottom of the list of objects.
Once you have found the object click the View Placement Details link to see in what servers and disks the object is placed. In the image below you can see that there are four components, each set of two in a fault domain of a strechted cluster, and that there is a witness per fault domain and a witness on the witness host.
Ruby vSphere Console will show the same information but also a little bit more. If you don't know how to access RVC then there are two good articles out there that will be helpful: link 1, link 2.
To show the object information in Rube vSphere Console you will need the objects' UUID. That can be found under the Services tab, have a look at the first picture in this article to see where to find it.
In Ruby vSphere Console use the cd command to access your cluster in the inventory. Once in the cluster folder execute the command vsan.object_info . <UUID>.
In this command the . (dot) is to represent the current object in the inventory if you are in the cluster's folder or else type the path to the cluster as a parameter.
If you take a look at the output below then you can see that the object placement is the same as in the graphical output but here it also shows the size of each of the components.