Manual Failover
You can configure your availability
group for automatic failover or for manual failover. In case of automatic
failover if the primary replica/instance does down the AlwaysOn
availability group switches the role of primary replica/instance to another synchronous
secondary replica.
You can also elect for
manual failover. The failover will occur without data loss if both primary and secondary replicas are
in synchronous commit mode and are in a healthy state, data loss will occur if the secondary
replica is in asynchronous commit availability mode. To do a manual failover
using the wizard, click on the Start Failover Wizard link on the top right
corner of the availability group dashboard as shown below:
This will
launch the failover wizard, the first screen of the wizard is the welcome screen
so click Next to proceed:
On the Select New Primary Replica
page of the Failover Availability Group wizard, you need to specify the
secondary replica which will be the new primary replica after the failover, the
screen will also display the failover readiness and availability mode (synchronous
or asynchronous). Click next continue:
On the Connect to Replica
page of the wizard, you need to connect to the
secondary replica which you want to make the primary replica after failover,
click on the Connect button to get connected to the secondary replica:
The Summary page of the
Failover Availability Group wizard will display a summary on your selection
and actions that wizard is going to perform. Click on Next to failover. You can also
generate the failover T-SQL script by clicking on Script button at the
bottom:
Clicking on Finish
will start switching the role or performing the failover, you can
monitor the progress and overall of status of operation as shown in screen
below:
If I open the availability group
dashboard again or refresh it, I can see role has now, my earlier
primary replica (ARSHAD-PC) is now the secondary replica whereas my earlier
secondary replica (ARSHAD-LP) is now the primary replica:
Please note, this example and
demonstration is based on SQL Server 2012 RC0 and there might be slight changes
in the RTM release; refer to BOL (Books online) or msdn for updated information.
Summary
In
this article I discussed the AlwaysOn availability group feature of SQL Server
2012. AlwaysOn is a new High Availability (HA) and Disaster Recovery (DR)
solution in SQL Server 2012 which improves high availability and protects data
of your mission critical applications. AlwaysOn availability group is
recommended over database mirroring since it combines the best of failover clustering
and database mirroring and overcomes the several limitations imposed in
failover clustering or database mirroring setup.
Resources
Overview of
AlwaysOn Availability Groups (SQL Server)
AlwaysOn Failover
Cluster Instances (FCI)
Overview of
PowerShell Cmdlets for AlwaysOn Availability Groups (SQL Server)
Overview of
Transact-SQL Statements for AlwaysOn Availability Groups
Monitor
Availability Groups (Transact-SQL)
Client Connectivity
and Application Failover (AlwaysOn Availability Groups)
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