You need to create a mirror copy of the database data on two machines with automatic switching. On host A — principal, for he wants to give B — mirror + witness. When you disconnect from the network, everything works with a Bang — mirror becomes principal'ohms, and I calmly continue to work with the database after reconnect. If you disable B, even if the database is on A was in the role of principal a, base on And goes into recovery mode and therefore not available. How to make A database to continue running when no communication with the witness?