Symlink/Hardlink for huge folder for application testing

We have an application that connects to a DMS which stores uploaded documents in the fileserver on the drive with subdirectory structure based on the year, entity id then document type. i.e. X:\DMS\year\entity_id\doc_type

From time to time we duplicate the DMS folder into our test environment (file is hosted on the same server but different drive) using robocopy to replicate certain production issues. The DMS folder has since grew to 40GB with 169k files.

It's very time consuming to do that now, hence we wanted to look for alternative. We're looking at using hardlink or symlink and just update them when there's new files added into the production DMS. Though any files added into the DMS of the test environment shouldn't appear back into the production one.

What is the recommended way to achieve this?