Feb
18
2012

What is Active/Active Cluster means in SQL Server World

Source: http://social.msdn.microsoft.com/Forums/en-US/sqldatabasemirroring/thread/b6787cbc-e165-4730-9fba-7898af1716a6/

MSCS (Microsoft Cluster Services) is not a load-balancing product, it is simply a high-availability solution.

Load balancing does not come in to play at all with clustering a Sql database…the term Active/Active seems to imply that this would be the case, which is why we typically try to refer to them as Multi-instance clusters now instead of the Active/Active label. Active/Active in the MSCS world basically means that you have 2 independent Sql Server instances running on 2 cluster nodes – these instances are independent of each other in all respects, obviously unless you link them in some manner with custom business logic, replication, etc. Think of them for all intents and purposes as 2 seperate instances running on seperate servers at all times (as that’s what they really are)…the only difference being that in case of a physical node failure (or service failure on a node), the instance will be moved to and hosted on a second physical server.

To support load-balancing, or scaling out in a Sql Server environment you have a couple of different options, depending on your edition, environment, version of Sql, etc. Take a look at the following articles for a start:

http://msdn2.microsoft.com/en-us/library/aa479364.aspx
http://www.microsoft.com/technet/prodtechnol/sql/2005/scddrtng.mspx


Useful links:
http://www.microsoft.com/technet/prodtechnol/sql/2000/deploy/hasog04.mspx
http://www.microsoft.com/technet/community/chats/trans/sql/sql0513.mspx
http://www.sql-server-performance.com/dk_massive_scalability.asp
http://www.sql-server-performance.com/articles/clustering/massive_scalability_p1.aspx


It is often overlooked the fact that SQL Server comes with a true load balancing capability available in ALL editions (including Express), with the know how to route related requests to the same node to avoid transaction replication and built-in support for high availability on each node. It costs nothing extra in licensing (other than the SQL instances licensing) and it scales by simple means of adding a new hardware and modifying one routing table, completely transparent to the application.

The only issue is that this load balancing is not designed for the TDS protocol (ie. T-SQL requests), but for the Service Broker protocol: Service Broker Routing Examples. If you can design your application in terms of SSB requests rather than T-SQL requests, you will be able to leverage this built in load balancing.

Hope you would like to read more about Service Broker, please do so and try to implement it if possible.

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About the Author: Nitin Garg

Indian born, trekker, biker, photographer, lover of monsoons... I love to blog the topics I research and find useful for self or online community to save time and energy :) Everything you read on my blog is my own personal opinion!

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