many Servers of SQL server 2012 needs mirroring
Automatic failover requires a witness. See Database Mirroring Witness:


  To support automatic failover, a database mirroring session must be configured in high-safety mode and also possess a third server instance, known as the witness. The witness is an optional instance of SQL Server that enables the mirror server in a high-safety mode session to recognize whether to initiate an automatic failover. Unlike the two partners, the witness does not serve the database. Supporting automatic failover is the only role of the witness.


Your application will also have to use a mirroring aware connection string, see Connect Clients to a Database Mirroring Session:


  "Server=Partner_A; Failover_Partner=Partner_B; Database=AdventureWorks; Network=dbmssocn"