The three types of failover options are automatic, manual, and forced service. Table 11.2 summarizes the availability of these options based on the mirroring mode and presence of a witness instance.
|Mirroring mode||Witness||Supported failover modes|
|High performance||No||Forced service|
|High safety||No||Manual or forced service|
|High safety||Yes||Automatic, manual, or forced service|
Let's begin this section with a look at automatic failover.
If the principal instance fails, automatic failover brings the mirror database online as the new principal database. For this to occur, all of the following conditions must be true:
Mirroring must be operating in ...