Best way to backup NC running in VMware

I recently installed NC on Ubuntu 18.04 in VMware Player, the Host is also Ubuntu 18.04.
I use the preinstalled NC 40GB bundle from www,
I’d like to use an external 500GB HDD for backup.
NC is used by 4 clients, just for saving and sharing pictures, office documents, some calendars and joplin notes and for chats and videochats (using NC Talk). It just runs during daytime.
The amount of stored data won’t exceed 20 GB.

What is the best way to backup NC ?