SQL Server 2012 as a Multisite DR Option

Question

I am looking on some input regarding the use of SQL Server 2012's AlwaysOn Availability Group feature as a multisite DR option to potentially replace costly SAN replication. Are there any practical or theoretical limits to the number of databases that could be replicated with this feature?

Thank you in advance.

Answer 1

Since AlwaysON is a combination of database mirroring and failover clustering, you can check these

http://msdn.microsoft.com/en-us/library/ff878487.aspx

Maximum number of availability groups and availability databases per computer: The actual number of databases and availability groups you can put on a computer (VM or physical) depends on the hardware and workload, but there is no enforced limit. Microsoft has extensively tested with 10 AGs and 100 DBs per physical machine.  Signs of overloaded systems can include, but are not limited to, worker thread exhaustion, slow response times for AlwaysOn system views and DMVs, and/or stalled dispatcher system dumps. Please make sure to thoroughly test your environment with a production-like workload to ensure it can handle peak workload capacity within your application SLAs. When considering SLAs be sure to consider load under failure conditions as well as expected response times.

http://support.microsoft.com/kb/2001270

http://sqlcat.com/sqlcat/b/technicalnotes/archive/2010/02/10/mirroring-a-large-number-of-databases-in-a-single-sql-server-instance.aspx

Answer 2

I am looking on some input regarding the use of SQL Server 2012's AlwaysOn Availability Group feature as a multisite DR option to potentially replace costly SAN replication. 

Based on my understanding with AlwaysOn you will still need a third party SAN Replication. 

Answer 3

There are two types of "AlwaysOn".  AlwaysOn Availability Groups and AlwaysOn Failover Clusters.  Both of these can be configured in a multisite configuration, but only AlwaysOn Availability Groups has built in replication.  AlwaysOn Failover Clusters in a multisite configuration requires either array based replication or host based replication solutions as described in my article here.

AlwaysOn Avalability Groups is a great solution and is included with the Enterprise Edition of SQL Server.  AlwaysOn Failover Clustering can be used in SQL Server Standard Edition (limited to 2 nodes) as well as SQL Enterprise Edition (unlimited nodes).

I wrote an article that compares and contrast AlwaysOn Availability Groups with AlwaysOn Failover Clusters in a multisite configuration here...

http://clusteringformeremortals.com/2012/04/05/sql-server-2012-standard-edition-availability-options/

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David A. Bermingham, MVP, Senior Technical Evangelist, SIOS Technology Corp

Answer 4

Thank you for this information - it will help me make a more informed decision about our eventual architecture.

Answer 5

Thank you for that information.