Smart backup :-)

There are no remote text files. The remote filenames and contents use a backup-specific format.

How the backup process works

See above. Overview also explains that Duplicati is not a file synchronization program (or a copy).

If some of this is just wording difficulties, and you mean you actually restored some source text file somewhere (for tests, preferably to a different folder without such a file), what exactly did you get?

sounds like a file-at-a-time copy is in mind. That’s far from what actually happens. See backup link.

This explains the process in more detail. Note that files are found at one end of the whole process, whereas uploads are at the extreme far end. Inability to upload a dblock file may affects many files.

The AFFECTED command is a way to find out which source files are affected by a given dblock file.
Disaster Recovery gives an example of this use after intentionally causing damage to a test backup.

Having said the above, I’m having trouble getting any quota message using various combinations of

  --quota-size (Size): A reported maximum storage
    This value can be used to set a known upper limit on the amount of space a
    backend has. If the backend reports the size itself, this value is
    ignored

 --quota-warning-threshold (Integer): Threshold for warning about low quota
    Sets a threshold for when to warn about the backend quota being nearly
    exceeded. It is given as a percentage, and a warning is generated if the
    amount of available quota is less than this percentage of the total
    backup size. If the backend does not report the quota information, this
    value will be ignored
    * default value: 10

with backends that seem to be reporting quota (visible in job log) and ones that do not. There may be bugs here, and you can file an issue if you like. I didn’t see one, so perhaps few people rely on quota.

Backing up to the auto-adapt idea, I’d be very nervous about trying to predict space need in the future because usage tends to grow either through more versions being kept, or more and bigger files made. The “smart” backup might wind up looking quite dumb when it automatically deletes precious backups.