Back up file smaller than source

Hi folks,

I’m running into a weird issue. I have a Duplicati job that backs up a full image of my raspberry pi to Backblaze B2. The image is not created via Duplicati, only the upload happens through it (AES encrypted, 10gb blocks)

As you can see in the screenshot below, the source size matches the .img file on the disk, but the backed up file(s) is significantly smaller. Can anyone provide some info or reading material on what might be happening here?

I do have a bug report (generated via Duplicati) but I’m not sure if I should be uploading it here? Thank you.


Duplicati runs data through a deduplication and compression engine, so it is definitely possible for the back end to be smaller.

You could restore the file to a different machine and then compare the size and sha checksum between it and the source file if you’d like to double check it.