I want to set up regular backups, and deja-dup seems like a nice tool. However, I want to put my backups on an extension USB drive that I have, not on a remote network location. Naturally, this drive is not always connected. If I configure deja-dup to backup to a directory on this drive (e.g. /media/extention/backup), what would happen? Will it prompt me to connect the drive when it is missing (the desired behavior), or just fail silently? Is there some way to tweak it to do so?

I can roll my own cron-based backup script that checks if this drive is mounted, but I would really prefer to use an existing, integrated tool.