Thank you for your post.
You are able to store container data securely on a secondary drive. For example, you might make the additional Database Folder Path on the C:/ and then the Container Data Path on the D:/. For more information on setting up additional database folder see page 75 of the FileMaker Server 14 Help Guide.
If it’s a new Database you can move the file to your new Database Folder Path on the C:/ and start adding data to the containers, which will be stored in your D:/ path. If there are already containers using External Data Storage you will need to move the Files Storage folder from Data > Databases > RC_Data_FMS > (FolderName) to your new Container Data Path on the D:/RC_Data_FMS/(FolderName).
You will not need to map the location via FileMaker Pro when using Secure Data Storage. For more information on storing container field data externally see Knowledge Base Article #10244.
I hope this information is of use!