If you plan to assign the role of a backup repository to Microsoft Windows Server 2016 version 1709 and later or Microsoft Windows 10 Pro for Workstations, mind the following limitations:
Fast Clone and Windows data deduplication cannot be used simultaneously. Thus, if you target a backup job to a repository supporting Fast Clone and enable Windows data deduplication, the Fast Clone technology will not be used for this job.
If you target a backup job to a CIFS ReFS repository and enable Windows data deduplication, the job will fail. Veeam Backup & Replication does not support such scenario.