Hello @TNO 

Thanks for the great question, there are two options you have here that i can see that have pro’s and con’s.

1- Use NDMP: https://documentation.commvault.com/2023e/expert/ndmp.html
PRO - Backups will be quite fast

CON - Restore of small amounts of files will be extremely slow

2- Use Files system agent: 
Windows: https://documentation.commvault.com/2023e/expert/microsoft_windows.html
Unix: https://documentation.commvault.com/2023e/expert/overview_unix_linux_file_systems.html
PRO - Restores and search will be much faster and consistent 

CON - First backup will be extremely slow with 300m file count ( multiple weeks for the first job  to complete ).

To save the pain of the file system agent, once you have that first backup you can run Syth fulls from there on out to save the ongoing pain. 
The feature Optimized scan will also help a lot of pain for the long term. 

https://documentation.commvault.com/2023e/expert/optimized_scan_for_file_systems.html

Kind regards
Albert Williams