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What happens when you fail over a mirror server?
During a manual failover, the principal and mirror server roles are swapped for the database on which the failover occurs. The mirror database becomes the principal database and the principal database becomes the mirror.
When to manually fail over a database mirroring session?
Manually Fail Over a Database Mirroring Session (SQL Server Management Studio) When the mirrored database is synchronized (that is, when the database is in the SYNCHRONIZED state), the database owner can initiate manual failover to the mirror server.
How to switch database mirror roles in SQL Server?
The principal server disconnects clients from the principal database, sends the tail of the log to the mirror server, and, in preparation for switching to the mirror role, sets the mirroring state to SYNCHRONIZING. The mirror server records the log sequence number (LSN) of the last log record received from the principal as the failover LSN.
What happens if failover fails in SQL Server?
If failover fails, an error message is displayed and the dialog box remains open. If you have modified any properties since opening the Mirroring page, those changes will not be saved. The dialog box closes automatically.
How to check the mirroring status of a database?
Connection status of the witness, preceded by a status icon, Unknown, Connected, or Disconnected. Click to display the history of mirroring on the server instance. This opens the Database Mirroring History dialog box, which displays the history of mirroring status and statistics for a mirrored database on a given server instance.
Why is the mirror database lagging behind the principal database?
The contents of the mirror database are lagging behind the contents of the principal database. The principal server instance is sending log records to the mirror server instance, which is applying the changes to the mirror database to roll it forward.
Why is MY SQL Server mirroring connection timed out?
The mirroring connection to “TCP://SQL01.DOMAIN.INET:5022” has timed out for database “Data” after 30 seconds without a response. Check the service and network connections. The mirrored database “Data” is changing roles from “PRINCIPAL” to “MIRROR” due to Role Syncronization.
How does a mirror server become a principal server?
The mirror server becomes the new principal server, and the former principal server becomes the new mirror server. The new principal server rolls back any uncommitted transactions and brings its copy of the database online as the principal database.
Can a database be made available to a mirror server?
On the loss of the principal server, the database owner can make the database available by forcing service to the mirror server (with possible data loss). We recommend that the WITNESS property be set to OFF in high-performance mode. Otherwise, to bring the database online, the mirror server must connected to the witness.
How to calculate the failover time for mirroring?
To estimate failover time, create a test database in the environment under which you intend to run mirroring. Then take a log backup from the production database. To measure the redo rate for that log backup, time how long it takes you to restore the log backup WITH NORECOVERY onto the test database.