Now the next question that comes in mind is about the single point of failure for witness. It is not a single point of failure because if witness fails, principal and mirror will still continue to form a quorum.
Various types of quorum are possible.
Say for example
A = Principal
B = Mirror
C = Witness
Full Quorum – Both partners and witness are included - A∩B∩C
Now that we know all possible types of quorum, let’s see how each one affects the database and application.
If witness is disconnected when either partner goes down, the database is unavailable since quorum cannot be formed. If the session loses quorum, then the database will not be available until the quorum is re-established.