Hello everyone! I just finished backing up a set of files worth about 900GB with Duplicati. I knew that a lot of huge files in that set were duplicates, so I was expecting a big difference between the “Source” and “Backup” size. Yet, I was surprised to find a huge difference between the “Source” size and the actual size of the files being backed up on disk:
Size on disk: ~900GB
Source size, reported by Duplicati: 357GB
Backup size: 315GB
How does Duplicati actually calculate these sizes? Given the disparity, I thought about two different hypotheses:
- Something went wrong with the backup (but as of now, I have now indication that it did).
- Duplicati already excludes duplicates from the “Source” size calculation, and the difference between “Source” size and “Backup” size is mainly due to compression.