To avoid data-loss it is important for you to backup your application data.
What Do I Need To Backup?
Everything in the configured DATA_PATH. Just copy and store.
How Is Data Stored?
Note Mark V1 stores your note data in a normal file/folder structure. It utilises a SQLite database for storing user details and the file/folder structure cache (called a tree-cache).
Here is a example of how data is stored at DATA_PATH:
/data
/db.sqlite
/notes
/leo
/my-note.md
/my-note
/my-asset.jpg
Restore
To restore you should just be able to copy all data back into the configured DATA_PATH.
If you happen to loose/corrupt the database file, you will need to copy just the notes folder and then create the users and run the clear-cache command from the CLI.