Microsoft has provided interactive data maps, which tells us about the geographic details, where customer data is stored for Microsoft Dynamics 365 for Sales, Customer Service, Field Service, and Project Service Automation.
Click on the below link to get more information.
Choose a Geo from the Geo dropdown to see the list of all Datacenters in that Geo.
For instance, i have selected India Geo and can see Pune and Chennai are the Data Centers, where the actual application data is stored.
Also, Azure Active Directory information stored in United States, Netherlands, Ireland, Singapore and Hong Kong.
Note: Microsoft replicates customer data in at least two datacenters at any given time for reliability and availability.
Hope this article helped you to understand about Dynamics 365 data storage.