Hey Ryan,
Thank you for your question and I'll provide more insight as to how the setup is facilitated.
Each single machine node of a Spatiotemporal cluster must be on its own server, and you'll need to install the ArcGIS Data Store program on each one. Once installation is complete, you can then use the web GUI that pops up to setup a new "Spatiotemporal" data store and register it to the same hosting ArcGIS Server. By registering each new node to the same ArcGIS Server, it effectively links all of them together and makes them available to receive data from GeoEvent.
The ArcGIS Server itself doesn't control the distribution of data among the nodes, rather it just acts as the middle man and sends commands down to the data store. Data replication, distribution and preparing it for querying is actually handled by the Spatiotemporal Data Store software itself. In a nutshell when each node is registered to the same ArcGIS Server site the software tracks the nodes, controls how the data is distributed and how fast it's available for query. The user doesn't have to modify or control anything, it's simply a matter of registering new data stores on separate machines that will participate in the cluster.
Hope this helps
- Chris