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Exchange Server transaction logs are a key part of the way Exchange backups work. If a transaction log is missing from a backup set, or not available in an online backup, the Exchange restore operation will not be able to complete.
Since Exchange transaction logs can eat up a lot of disk space though, administrators often wonder if it's possible to selectively delete transaction logs that are no longer needed for Exchange restore operations.
One option that can reduce the amount of space used by Exchange transaction logs is circular logging, where the oldest logs are eventually overwritten as they're phased out. Unfortunately, circular logging makes it impossible to run incremental backups and differential backups on Exchange Server stores using an Exchange-aware backup product, so it's impractical for many shops.
Another possibility is to judiciously remove unneeded Exchange transaction logs. Although Microsoft doesn't recommend it, there is a way to find out manually which transaction logs are no longer needed by determining the last checkpoint created by an Exchange Server backup.
To do this from a command line, go to the \Program Files\Exchsvr\bin directory on the server and run the following command:
eseutil /mk "C:\Program Files\Exchsrvr\MDBDATA\E00.chk"
(The quotes are important, as they delimit the full pathname for the file.)
In the results returned you'll see these lines:
The first number in the "Checkpoint" entry -- 0x2 -- is a hexadecimal number that refers to the last checkpoint log. Therefore, any logs numbered E000001.log or earlier could be removed. If the checkpoint was 0x14C8, then logs numbered E0014C7.log or earlier could be removed.
If you're leery about erasing Exchange transaction logs completely, you can always compress them and move them offline instead.
About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter.
Related information from SearchExchange.com:
- Tip: Clearning the confusion around Exchange Server circular logging
- Tip: Structuring Exchange Server for the best log file protection
- Tip: Backing up, truncating and cleaning up Exchange transaction logs
- 10 tips in 10 minutes: Fundamentals of Exchange Server disaster recovery
- Reference Center: Exchange transaction log tips and resources
Dig Deeper on Microsoft Exchange Server Transaction Log Files