Microsoft® SQL Server 2012 Unleashed

Database Mirroring Operating Modes

With database mirroring, you have the option of deploying in one of three modes: high safety with automatic failover mode (high availability with a witness server), high safety without automatic failover mode (high protection without a witness server), and high-performance mode. Each mode has different failure and protection characteristics and uses the database mirroring configurations slightly differently. As you might expect, the high-performance mode offers the least amount of protection; you must sacrifice levels of protection for performance.

Database mirroring runs with either asynchronous or synchronous operations:

Synchronous operations—With synchronous operations, a committed transaction is committed ...