Q

Should I enable Exchange 2010 circular logging?

A novice administrator is curious if he should enable Exchange 2010 circular logging. Our expert offers his thoughts.

My company recently migrated to Exchange Server 2010. I'm relatively new and unsure whether we should use Exchange...

2010 circular logging or not. Can you please advise?

Before I answer the question, you should first understand that Exchange Server 2010 uses two separate types of circular logging.

The first type is known as database-level circular logging. It has been available in Exchange Server since version 4.0. The other type of circular logging available in Exchange 2010 is a specialized type that is solely used in database availability groups.

When it comes to using the first type of Exchange 2010 circular logging, my recommendation -- as well as Microsoft's -- is simple: Do not use it. Enabling circular logging allows transaction logs to be overwritten after their contents have been committed to the database. In short, this is not something you want happening.

Back in Exchange 4.0, circular logging was a welcome feature because storage space was so expensive. Today, storage space is cheap. Therefore, it doesn't really make sense to enable circular logging in the name of saving space. As previously mentioned, circular logging also overwrites transaction logs. This is important to understand because it prevents you from accomplishing point-in-time disaster recovery.

About the author
Brien Posey is an eight-time Microsoft MVP with two decades of IT experience. Before becoming a freelance technical writer, Brien worked as a chief information officer at a national chain of hospitals and health care facilities. He has also served as a network administrator for some of the nation's largest insurance companies and for the Department of Defense at Fort Knox.

This was last published in January 2013

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But if you follow Microsoft's guidelines and kick out the backup and start using the LAG databases. (assuming that you do not need to restore over 14 days data). Then is there any reasons to no enalbe circular logging?
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The pupose of the DAG is to provide high availability by using multiple copies of the data. Once a transaction log has been committed to all database copies it is no longer of use. The only possible time a transaction log may be needed again is if you want to do a point in time restore, but if you are required to perform these restores you should be doing incremental backups using something like DPM.
Therefore transaction logs after being committed are a waste of space on all your database disks and in your backups.
Turn on Circular Logging and make your life easier!
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