Suneido does not have any built-in replication features for the database (not yet anyway).
There has been some work done on ODBC connections and MySQL interfaces from Suneido. You can find them here:
Quite a few of the downloads available on the page have not maintained with every release of Suneido therefore some may not work with the current download of Suneido.
One way of doing a backup while Suneido is running is to use the Dump() function. If you call it with no table argument, it makes a dump of the entire database to your current working directory. This type of backup wouldn’t work as a real-time solution since it is dumping the entire database when you call Dump(). Since it is dealing with the entire database it is not something you want to be calling too frequently.