How to mount a external disk by systemd

sudo vim /etc/systemd/system/backup.mount

[Unit]
Description=Backup Hard Driver mount
After=network.target wpa_supplicant.service

[Mount]
What=/dev/disk/by-label/backup
Where=/backup
Type=ext4
Options=defaults

[Install]
WantedBy=multi-user.target

sudo systemctl daemon-reload

sudo systemctl start backup.mount