A discussion about the discrepancy between total backup size and total upload size has raised questions about the logic behind it. UnicornX shared screenshots showing the difference in sizes and sought clarification.
Ed_S suggested that compression could be the reason for the smaller backup size. gerhard explained that backups do not contain thumbnails by default, which are included in the total upload size.
UnicornX sought confirmation that this discrepancy is normal, which was confirmed by Ed_S. Ed_S shared their own experience where the backup size was smaller than the upload size due to the exclusion of optimized images (thumbnails) from backups. Ed_S also referenced a quote from supermathie explaining that the storage of multiple image versions is a trade-off for faster client-side loading and memory efficiency.
By default, backups so not contain thumbnails, because they can be recreated. But the total upload size shown in the dashboard includes the disk usage of thumbnails.
Edit: yes, it’s normal, and it’s true for me too: uploads reported as 1.2G and a backup is 750M. I’ve checked my backups, and they include uploads/default/original but not uploads/default/optimized, which is as expected.
Edit: I see now that “thumbnails” is a misnomer - it’s a collection of pre-processed versions of original images, and can be larger than the originals. See for example