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While migrating mailboxes from Exchange 2003 to Exchange 2007, the Exchange 2007 transaction logs filled the drive causing the data stores to go offline. My theory is the Exchange 2007 mailbox migration process floods the logs with migration log entries.

I'd like to delete any transaction log entries that are no longer needed, freeing space for more transactions to occur.

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up vote 3 down vote accepted

The recommended method is to back up your Exchange server. That will remove the logs as long as you are using a supported backup application for Exchange. You should also make sure that you have enough room for the transaction logs. They can be moved to another drive if you are running out of space.

You should be aware that enabling circular logging is a dangerous setting in a production environment because you can put yourself in a position where you cannot recover your Exchange database because previously backed up transactions had been over-written and not saved in the backup.

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Thanks, and good blog content. Got a twitter account I can follow? I'm @JimStraatman – Jim Straatman Jan 2 '10 at 22:13

Resolved by enabling circular logging during the migration process.

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+1. I wish I would have seen this post earlier. The problem that occurs when moving mailboxes is that Exchange logs the move operations to the transaction logs while the moves are in process. You can't backup the transaction logs in order to truncate them while the move is in process and you risk running out of disk space during the move. The only effective way of dealing with this is to temporarily enable circular logging during the move and disabling it again after the move. – joeqwerty Jan 3 '10 at 6:04

I found this article which may be helpful in case there is problem with the log disk filling up:

hope that helps.

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