Assume you have 10 TB HDD in your Ubuntu 16.04 installation. You are copying documents from external HDD at rate 30 Mb/s to your Ubuntu harddisk. It will be lasting so long time that it will not be at the end, until the laptop is put to the backpack next time. You want to start backupping of the system.
How well can Deja Dup handle concurrent processes with Ubuntu? What will Deja Dup do with new files and partial files coming to the system during the full system backup?