Interview: SQL Server 2012 AlwaysOn Availability Groups

published: 2013-03-08 00:00

Below is a Q&A interview conducted with Sean Young and Leigh Verhave in relation to SQL Server 2012 Availability Groups. Sean Young is the principal SQL Server Consultant at RockSolid SQL and Leigh is a senior SQL Server consultant within the same team.


Q. What are SQL Server 2012 AlwaysOn Availability Groups?

[Sean] An Availability Group is a number of user databases consisting of up to 100 databases. It allows you to fail over a group of databases rather than a single database. It differs from database mirroring and log shipping as they are configured at a single database level. It’s a disaster recovery & high availability solution in one.


Q. How do SQL Server AlwaysOn Availability Groups differ from technologies include in SQL Server 2008 R2 and below?

[Sean] To get both a high availability and disaster recovery solution often requires you to implement a mixture of SQL Server 2008 R2 features. For example, a typical setup would use clustering for high availability and log shipping for disaster recovery. AlwaysOn Availability Groups provide you with high availability & disaster recovery in one solution.

[Leigh] Database mirroring and log shipping are only available at an individual database level and a multi database application will not failover seamlessly under normal circumstances.


Q. What is the #1 key benefit of SQL Server AlwaysOn Availability Groups?

[Sean] One complete solution offering both 100% uptime and data protection.

[Leigh] Being able to configure a highly available solution for a group of databases but also have the option of using one or all the secondary replica as a read only reporting platform on LIVE data.


Q. When should you consider using SQL Server AlwaysOn Availability Groups?

[Sean] It depends on the business requirements. If the business wants little or no downtime along with data protection then this functionality should be considered. You will need a SQL Server Enterprise Edition license and Windows Server Failover Clustering configured. Although it may take some time to setup the benefits post setup, in my opinion, make it worthwhile.

[Leigh] When a mission critical application relies on a suite of databases that are required to be both highly available and protected from disaster.


Q. When should you not consider using SQL Server AlwaysOn Availability Groups?

[Sean] If you don’t have a SQL Server Enterprise license and no budget to purchase one. Also if your business can cope with downtime and small amounts of data loss there are other cheaper options.

[Leigh] To reap the benefits of always on high availability groups with no data loss, synchronous data transfer is required. This can negatively impact performance on very high load OLTP systems, in that case it might be better to configure with asynchronous data transfer, this inherently has a chance of data loss.


Q. What are the edition and licensing requirements to run SQL Server AlwaysOn Availability Groups?

[Sean] You need a SQL Server Enterprise license. You also need a Windows Enterprise license for the clustering technology.


Q. What are any other considerations in relation to use of SQL Server AlwaysOn Availability Groups?

[Sean] Determine the business requirement & costs. Then look at the options available to you. I feel that this new SQL Server feature offers tremendous benefits.

[Leigh] The always on high availability replicas do not replace the need for a robust backup plan – always maintain backing up your databases as you require.

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