I'm looking for a database (DBMS) that is easy to scale out. I would like to have high availability so I need a multi-master cluster, where the data is replicated to two or more physical computers. I would also like to be able to start with one node (no replication), and then scale out to more nodes as needed without a reinstallation or downtime.
I would like to have a DBMS that are easy to maintain and manage. It should be easy to add nodes, remove nodes, take live backup and monitor the use of resources.
It doesn't have to be a relational database system, so a NoSQL is okey. And I would like to have a free version so I can test it in small scale and compare it with alternatives.
What alternatives do I have?