I have some important files that I am backing up via 2 seperate mechanisms to the same file storage. In my particular case, this is a backup of Microsoft Teams files via 2 different mechanisms :-
Using onedrive on a PCs and then a backup with duplicacy with the files downloaded, and
QNAP NAS and HBS to sync the files from teams, and then Duplicacy to backup the files.
In both cases, the synced files on the PC and NAS is about 27GB. I only setup the QNAP option today, and because they are effectively pretty much exactly the same files, I would not have expected the size on the backup storage to change much, because I would expect Deduplication to do its things, for small incremental increase in the backup. However, I was a bit surprised to see some significant transfers and it appears over 2.5GB of additional space was needed. For reference the backup is about 48000 files and 2620 directories. But again largely the same on both backups.
Is this to be expected, and why is it not closer to zero size increase?