Is your 8TB mounted somewhere and this place has being added as external storage local folder? If yes, then:
- Stop your server and make DB backup.
- Copy your Private data to the RAID to some subfolder, e.g. myData
- Unmount your 8TB USB
- Mount your myData folder from the RAID to the same place as it was mounted as it was 8TB USB.
- Start the server run rescan command:
sudo -u www-data occ files:scan --path user_id/files/8TBmount_nameand check if it works afterwards.
If it does not work: stop the server, restore DB and mount 8TB back 
You can also try to use NC Client:
- Syn folders from 8TB
- Move them locally to “RAID” Folder and Client should do the job. In this case shared links must be saved. Be aware about this ticket: