Comment 78 for bug 1217959

I've worked around this by using a bind mount instead of a symlink. Something like 'sudo mount --rbind /run/media/daboross/external/deja-dup-cache ~/.cache/deja-dup' works. While I do have to re-do this every time I mount the external drive and start a backup, it at least works.

If you also do a `chmod 500 ~/.cache/deja-dup` when it's unmounted, deja-dup will be unable to write any files to the unmounted directory and it will fail early - so you can then mount it and re-start the backup.