What is the difference between having a master-slave replication and having a master-master( where in the second master acting as hot-standby - active-passive) replication? Also, what are the issues that I could face having a master master replication where both the masters are writable. I have read here that experts have said it is very dangerous to have both masters writable. Without Percona/NDB/DRBD, what are my options for setting up HA for my databases? What is the best replication that I can have?