MySql cluster data node replication
MySQL Cluster automatically replicates data nodes, based on the number of replicas and the number of data nodes you specify.  Your tables are automatically sharded across these nodes, and updates are replicated between them for HA.

Worth watching the short demo to see more:
http://www.oracle.com/pls/ebn/swf_viewer.load?p_shows_id=11464419

For more detail - take a look at the 'Cluster overview' section of the docs:
http://dev.mysql.com/doc/refman/5.5/en/mysql-cluster-basics.html