I tried to find if similar topic was discussed before. I am using mirror backup from one 4 TB HDD (having 50% data) to another 5TB HDD, took me about 6 Hrs for the first time backing up, everything seems fine

Next day I added one image file in a folder of the source drive. I was having impression that if I click back up it should back up only that file, but that is not what is happening

