Mirror to multiple databases

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I currently have an instance of MySql persisting the content of the space using the default Hibernate implementation bean (DefaultHibernateSpaceSynchronizationEndpointFactoryBean), but I was wondering if I can persist the same data to other PostgreSql or Oracle11g instances at the same time. I know that there is a limit of one mirror-pu instance, but I'm not sure if that limitation is only per space (only one mirror persisting one space?) or per grid. So, how could I persist the same data to more than one database at the same time reusing the current hibernate annotations and configuration? Thanks.