The offering from Vision Solutions is (arguably potentially) interesting because CloudStack has some disaster recovery functionality built in, but it is not “real time” – it’s based on snapshots.
The Apache website feature lists confirms that, “To help mitigate data loss and a way of disaster recovery, users are given the capability of either taking adhoc snapshots of their disk volumes or setting up a comprehensive schedule for taking periodic snapshots of their data. Users can set limits to the number of snapshots taken to creating new data disk volumes from existing snapshots.”