Relational Junction for Salesforce will mirror your Salesforce data to Microsoft SQL Server, Oracle, MySQL, PostGreSQL, DB2, Sybase. It doesn't make any difference where the actual database is housed, but the Relational Junction server must be in the same Local Area Network to get reasonable performance. Sending data over the internet one record at a time doesn't scale very well. If you are going to use a collocated service, ensure that the database and the Relational Junction server are not in different data centers. Some of the services do not guarantee this.