Good news and/or perhaps already known to many.
It is recommended that you always have a back-up of Nas music files on a external disk, even if your Nas is equipped with two hard disks.
Today I did a test with Hyper Back-Up at Synology Nas
Determination (which is good news):
If you delete an album or folder from the original folder of your NAS, it will also be deleted from your backup disk after a new backup.
If you change the taging of an album on your NAS, it will also be adapted to the album of your backup disk after backup.
I just wanted to report this info