Under the default setup of Windows 2012 the group policy for folder redirection gives users exclusive rights to their files. This means that that user's documents are redirected, and stored, on the server. Because of this, backing up the server will not backup those files. Since the files are not on the workstation, backing up the workstation will not backup the documents either.
Under a typical setup of Windows 2012 Essentials, how are the user's documents suppose to be backed up?