Home > SQL Server, SQL Server 2012 > Know the cost of SQL Server 2012’s AlwaysOn Availability Groups

Know the cost of SQL Server 2012’s AlwaysOn Availability Groups

SQL Server 2012 takes Database Mirroring to the next level. Many of us have used SQL Server 2008’s Database Mirroring as part of a disaster recovery (DR) solution. And it’s serves well in that capacity (unless you try and use synchronous mirroring on a high usage DB across to another data center – trust me, don’t do that!).

Some of the great improvements with the touted replacement to Database Mirroring:

  • Can have up to 4 replicas (not just one)
  • Can failover multiple databases as a unit (not just one)
  • Can read from the replicas

However, don’t just blindly go in for this model without counting the cost. There are some requirements for this new technology that impact your licensing cost, and possibly administration cost. Here they are:

1) The feature requires Windows failover clustering – this means you’ll need the Enterprise edition or higher of Windows Server. A Windows cluster requires a minimum of two servers, and since your replica must be on a separate cluster, you’re talking 4 servers, at least. NOTE that there is no requirement to install SQL Server as a clustered application.

2) The feature requires SQL Server Enterprise Edition. See this article for a comparison of the various editions: http://www.microsoft.com/sqlserver/en/us/future-editions/sql2012-editions.aspx

Now the question arises: Is Database Mirroring still available as an option in SQL Server 2012? The answer is yes. But beware that AlwaysOn is the replacement and Database Mirroring will likely disappear in the next release. This is explained in the AlwaysOn FAQ here: http://msdn.microsoft.com/en-us/sqlserver/gg508768#OtherEnhancements

My suggestion is to give careful thought to your DR design BEFORE you make firm decisions on your hardware and software editions. You don’t want to be painted into a corner with Standard edition if you could really benefit from features like this which requires Enterprise Edition, and of course on the flip side if Database Mirroring is sufficient for your needs, then you might be just fine with Standard Edition.

Reference for this post:

Introducing SQL Server 2012’s AlwaysOn Availability Groups SQL Server Magazine, January 2012

http://www.sqlmag.com/article/sqlserverdenali/sql-server-2012-configure-alwayson-141127

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