Mountability checks are failing for protected system running Windows Server 2016 with ReFS file system and Exchange 2016.
The UI error:
Mail store 'ExDisk14Db' is not mountable. Error: 'The volume does not contain a recognized file system. Please make sure that all required file system drivers are loaded and that the volume is not corrupted. '
Microsoft operating systems can only mount ReFS volumes from an equal or lower operating system. This is not a product limitation, but a Microsoft operating system limitation. The table shown in the ReFS Wikipedia page, shows ReFS version comparability. To summarize, ReFS versions are backwards compatible form newest to oldest, but are not forward compatible.
Any job that requires mounting a ReFS recovery point from an operating system higher than the core operating system will fail. Jobs in include, but are not limited too:
This issue has been assigned change tracking ID RR-103698.