You can use the Server app to change the data storage location for all services. By default, all service data is stored in /Library/Server on the boot partition of the disk on which you installed the Server app.
Select your server in the Server app sidebar, then click Settings.
Click the Edit button to the right of Service Data.
Select the disk you want to use for service data storage, then click Choose.
When you change the disk used for service data, the Server app stops all services and copies the data for the services to the disk you chose. The Server app doesn’t delete service data at its old location.
Users can access the services again after the Server app finishes copying service data.