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Cicular Logging

Posted on 2011-03-21
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This question isn't so much to determine a correct answer, but more gauging opinions as to the right course of action.
The 2007 Exchange server at this organisation has multiple ways of recovering data.  The mailbox server role is clustered across 3 servers.  Each server points to a single SAN containing the mailboxes and logs for exchange, and that SAN is replicated to another SAN that is offsite in case of a DR scenario.  Mail is also archived in the cloud before reaching this Exchange server and all mail sent internally is processed through journaling and sent to the cloud providing full availability should this Exchange server go down.
Although the solution above provides high availability and the ability to restore the data should one of the SANS go down, transaction logs are not committed to the database and thereby not flushed.  To achieve this, monthly archives are done by backing up the databases to a disc locally.
What are people’s opinions on using circular logging in this situation instead of backing up?  For example, is the culmination of log files still necessary, or is it ok to overwrite the existing log files in a live environment?  Are there performance issues people are aware of that come to light after enabling circular logging for long periods of time?
Any help and opinions would be most helpful.
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Question by:OctInv
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by:Amit
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You can sign up and read below article

http://searchexchange.techtarget.com/tip/Clearing-the-confusion-around-Exchange-Server-circular-logging

My recommendation, not to use circular logging for Mailbox servers and always do full + Incremental backup. This will flush the logs. But recovery is slow. If you use differential backup. You need more disk space to keep the logs, as logs are not purged by diff backup. But recovery is fast.

For more detail read this
http://www.exchangeinbox.com/article.aspx?i=137
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1. Here is a good summary article on the subject http://support.microsoft.com/kb/147524
2. If you are running 2007 and CCR you will not be able to run circular logging http://msdn.microsoft.com/en-us/library/aa579094(v=exchg.140).aspx

3. The only times I use circular logging are

A: When I am doing a large import or mailbox migration and as soon as I am done I turn it off and kick off a full backup immediately
B:  disk space is low because I forgot to enable it when doing an IMPORT or MIGRATION OR something happens where my backups are failing and I am about to run out of disk space so I MAY turn it on to clear the logs and then off to get the backups done but that is really a very rare exception and most of the time its better to let the backup truncate the logs

4. here is another good article & recent for review on the subject http://blogs.technet.com/b/exchange/archive/2010/08/18/3410672.aspx
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by:OctInv
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I'll split the points here because I'm grateful for both your opinions.  However, amitkulshrestha's articles point more to Exchange 2003 and below, rather than the Exchange 2007 version I have here.

I really appreciate both your comments there so thank you.  Having said this, the advice and articles very much point to the recommendations not to have circular logging enabled, but I still can't really see a firm reason why when backups are not the concern?

I run clustering in SCC instead so circular logging is not a problem as well as having replications and snapshots of the databases stored in multiple physical locations, so backups are not necessary.  We still backup the databases at the moment for the sole purpose of flushing the logs, so I think we'll continue doing that until it is confirmed that circular logging is never going to be an issue.

Thanks again.
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by:lucid8
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In the end to do or not do circular logging is really a personal choice dependent upon the needs of your organization. As long as you know the pros and cons of doing so you are in a much better place to determine the appropriate configuration  

 Happy to be of assistance and thanks for the points
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