This section explains some of the underlying concepts on how darktable organizes images in the lighttable.
The basic element for organizing images in darktable is called a film roll – a kind of virtual folder. Whenever you import images from disk, the images are organized in a film roll whose name is derived from the name of the disk folder. Re-importing a disk folder will add any new images to the existing film roll; images already present in the film roll are not touched.
It is important to note that importing images in darktable does not involve a physical copy step. Importing a folder into darktable is therefore not a backup operation of that folder.