Multiple database servers for performance vs failover
If you are using mySQL, and you are not concerned about possible differences between your two databases, albeit for a short while, you could just set up mySQL Replication. 

This is different to the active-active clustering you have asked about.  Active-active clustering implies that 2 or more nodes are actively hosting services, but in a mySQL / SQL Server context, you will not have explicit "synched" data in they way you mean. Instead this could be better achieved by replication or SQL2012 AlwaysOn (if you considered using it).