Database Reference
In-Depth Information
AlwaysOn Availability Groups
AlwaysOn Availability Groups was a new feature in SQL Server 2012 and was a major
factor in certain shops while making the decision to migrate to SQL Server 2012. In
SQL Server 2014, there have been some major enhancements and improvements in
AlwaysOn Availability Groups. This includes allowing a replica to reside on Microsoft
Azure Virtual Machine to help maintain replicas across different data centers,
which have built-in disaster recovery as well, thus making use of the cloud, and also
expanding the number of replicas that can be included in your Availability Group.
In this chapter, you will learn about:
• Availability Group enhancements in SQL Server 2014, including the fact you
can have an eight node Availability Group
• Using Microsoft Azure Virtual Machines as replicas
• Troubleshooting Availability Groups
• Creating a hybrid Availability Group
Introducing AlwaysOn Availability Groups
AlwaysOn Availability Groups, introduced with the release of SQL Server 2012,
are best described as enhanced database mirroring. It allows a set of user databases
to failover automatically between different instances installed on separate servers;
these are commonly known as replicas. Thus, it provides both high availability
and disaster recovery, and applications that use these databases are automatically
redirected; this minimizes the application downtime. From a disaster recovery
perspective, multiple copies of the databases are maintained. So, if you have your
AlwaysOn Availability Group replicas dispersed across different sites, then you can
make use of the multiple database replicas for disaster recovery; if you lose one site,
your database and its data are also stored safely on the other site or sites.
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