@drakar2007 is correct - using the --backup-test-samples parameter you can adjust the number of filesets downloaded to something other than the default of 1. (Setting it to 0 will cause NO testing to happen.)
--backup-test-samples
After a backup is completed, some files are selected for verification on the remote backend. Use this option to change how many. If this value is set to 0 or the option --no-backend-verification is set, no remote files are verified
Default value: “1”
Note that this tests a fileSET so leaving it at the default of 1 means it will actually download and test 3 files - a dindex, dlist, and dblock file. The dblock is by far the largest (that’s your “Upload volume size”) with dindex and dlist files usually being under 1M each.
It has been noted that with larger backups / smaller dblock (Upload volume) sizes / less frequent backup runs it’s possible to be (by default) testing a single fileset per even if you’re adding MORE than one per backup run. This means that, while useful to have, Duplicati may never “catch up” and actually test EVERY uploaded file.
It’s been suggested that the parameter should be able to take a percentage instead of a hard integer. If you feel like chiming in on that, feel free to check out the topic at Should test / verify commands & --backup-test-samples support percentage parameter?.
I assume you mean dblock (Upload volume size) not ACTUAL block (as in file chunk) size… 