MS SQL database migration | Talk Web Hosting

500 GB in size, is it the size of the databases or the dump of the databases? Because it's about the size of the online databases, the dump should be considerably smaller and you might be able to move the data into the 9-hour downtime window , in the traditional way (dump> move> restore).

You can technically move all data without interruption, if you control both servers, by configuring a "master-slave" mysql replication. But this would require that you can adjust the mysql configurations on both the old and the new server, in order to configure the replication (that is, not on the shared hosting).