They may be occasions where it is required to mount the DRBD device at boot outside of pacemaker. While not common, we can accomplish this via a systemd unit file.
Usually, this isn't regarded as a best practice, but there may be some occasions where this is applicable and desired.
In this example we'll mount /dev/drbd0 on /drbd/r0 upon boot. Create a systemd unit file named /etc/systemd/system/drbd-r0.mount (you must name it with the mount path as the name, substituting dashes for slashes). The contents of this unit file should look like the example below:
Description=Mount DRBD device
Lastly, make sure you've enabled DRBD and this custom systemd unit at boot.
# systemctl daemon-reload
# systemctl enable drbd.service drbd-r0.mount
Reviewed 2020/11/30 - DGT