@marcoi @olivierlambert OK, I think I've found the problem, and a fix... at least for the error I was seeing...
- If you create a new backup with the method Delta Backup, it will fail with the error posted previously.
- Activate the "Use NBD to transfer disk if available" switch
- Save the backup job
- Deactivate the "Use NBD to transfer disk if available" switch
- Save the backup job
- Run the backup job again
This time, journalctl doesn't log any errors, and the export task can be seen:
My guess is, that even though by default the "Use NBD to transfer disk if available" switch is shown as inactive when creating a new backup job...
...in reality NBD is switched on by default. Activating and deactivating the switch presumably creates an entry in the job that specifies NBD shouldn't be used.
It would be interesting to know if anyone else can replicate this behaviour, or if it's just something odd in my setup?
