Initialize annex repository

mkdir ~/annex
cd ~/annex
git init
git annex init
git commit --allow-empty -m "init"

Add external drive as remote

git annex initremote music type=directory directory=/home/cashmere/music encryption=none importtree=yes

Import files into annex

git annex import master:music --from music
git merge music/master --allow-unrelated-histories

Setup external storage

git annex initremote storagebox type=rsync rsyncurl=u508334@u508334.your-storagebox.de:music encryption=none
git config remote.storagebox.annex-rsync-transport "ssh -p 23"

Backup to external storage

git annex copy --to storagebox