iCloud as a Backup
If you have the full Diarly version and iCloud sync enabled, all your data is replicated on the Apple iCloud service, so data is safe in case of computer hard drive failure or other difficulties.
Also, to prevent any accidental removal or to have your data safely stored on an additional drive, you can use Diarly Markdown exporter.
You can use the exporter by going to:
File > Export > Diarly (markdown)
Settings > Export > Diarly (markdown).
This file can then be later imported back to Diarly or easily opened in any text editor.
Please Note: When you later import markdown entries into the app, it will skip/ignore those which already exist so that your data is not overwritten.