Per ragioni di distribuzione geografica, per alta disponibilità e per considerazioni di prestazioni di accesso ai contenuti di SharePoint, è possibile realizzare una struttura in mirroring dei DB di SharePoint su SQL Server.

Queste un estratto delle motivazioni, recuperato dal whitepaper pubblicato su Technet:

• High-availability
  This operating mode allows you to synchronize writing transaction logs to both servers and enables automated failover. For this option to work, you must also have a witness server.
• High-safety
  This operating mode allows you to synchronize writing transaction logs to both servers, but failover is manual. Because automated failover is not part of this option, a witness server is not used.
• High-performance
  This operating mode does not synchronize writing transaction logs to the servers, and therefore offers some performance gains. When using this option, you are just assuming that everything is going to complete successfully on the mirror. This option only allows manual failover, and a witness server is not used.

Questo il link al whitepaper sul tema.