In the case you put all your data in the admin database (you shouldn't), you'll notice db.copyDatabase()
won't work because your user requires a lot of privileges you probably don't want to give it. Here is a script to copy the database manually:
use old_db
db.getCollectionNames().forEach(function(collName) {
db[collName].find().forEach(function(d){
db.getSiblingDB('new_db')[collName].insert(d);
})
});