Include Witness Server (Configure Database Mirroring Security Wizard)
Use this page to specify whether you want to include a witness server in this security configuration for database mirroring.
To configure database mirroring by using SQL Server Management Studio
Click to include a witness server instance in the security configuration. The witness is necessary for high-safety mode with automatic failover, which supports automatic failover to the mirror server instance if the principal server instance fails.
Click to configure security without a witness.