Comment 4 for bug 1077944

Probably the message "Not enough disk space" appears because the cache directory of deja-dup - which can get very big - fills up your internal disk.

The cache directory is located in ~/.cache/deja-dup. Move this directory to your USB-Drive and create a symlink to workaround the problem e.g.:

mv ~/.cache/deja-dup /media/usbdrive
ln -s /media/usbdrive/deja-dup ~/.cache/deja-dup