Disclaimer: “Fast howto” means in my world just dumping my config files for everyone to use, explanations are optional.

Used tools: systemd, rsync (and cryptsetup)

Just write a systemd service file like my ‘projectBackup.service’:

You can replace ‘projects’ with whatever you like/need.

[Unit]
#device file in question look for it with:
#systemctl --all --full | grep plugged
#you could also use uuid's which would be safer
#following is just my case:
After=dev-mapper-projects.device

[Service]
# script to start
ExecStart=/root/projectBackup.sh

[Install]
#obvious
WantedBy=dev-mapper-projects.device

The script:

#!/bin/bash

#just mount it...
mount /dev/mapper/projects /mnt/backup
#the magic happens here...
rsync -avhim --partial --exclude '**/tmp/**' /mnt/somewhere/projects/ /mnt/backup
# we're done so get da fuq out!
umount /mnt/backup
# hide my data... :)
cryptsetup luksClose /dev/mapper/projects

The only thing I’ve still to do after plugging the hdd in is:

cryptsetup luksOpen /dev/sdd1 projects

Everything else goes by itself. Of course you have no progress bar or whatever to know when it’s done. But you can use

journalctl -fu projectBackup.service

and you see all output of rsync like when you see it in your terminal when you run that command manually plus a really nice timestamp.