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Exchange transaction logs are written to a compressed folder

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at http://go.microsoft.com/fwlink/?linkid=34707.]  

Topic Last Modified: 2007-01-05

The Microsoft® Exchange Server Analyzer Tool queries the Win32_Directory Microsoft Windows® Management Instrumentation (WMI) class to determine the value of the Compressed key for the folder containing the Exchange information store transaction logs. If the value for Compressed is set to True for this folder, an error is displayed.

When a message is delivered to Exchange, it is first written to the transaction logs before it is committed to the store and delivered. On an Exchange 2000 Server or an Exchange Server 2003 computer, the transaction logs are written to the following default location:

<drive>:\Program Files\Exchsrvr\mdbdata

On an Exchange Server 2007 computer, the transaction logs are written to the following default location:

<drive>:\Program Files\Microsoft\Exchange Server\Mailbox\<Storage Group Name>

Microsoft does not support the storage of Exchange data files on an NTFS compressed volume. When you store your Exchange data files on a compressed volume, the additional overhead significantly impacts the performance of Exchange. In addition, after an information store database reaches a certain size (approximately 4 GB), it may fail to mount or it may become corrupt.

The Exchange data files include all the following files:

  • .edb files

  • .stm files

  • .log files

  • .dat files

  • .eml files

  • .chk files

Files that are managed by Extensible Storage Engine (ESE) are not designed to be stored on a compressed drive. The ESE depends on sector independence for log-based recovery, and compression of files invalidates sector independence. Compression should not be turned on for volumes hosting ESE databases, or any database that uses write-ahead logging.

Before Exchange 2000 Server Service Pack 3, compressed information store databases were allowed to mount. However, corruption can result in any Exchange 2000 Server information store databases or information store logs that have been compressed by using NTFS compression.

With Exchange 2000 Server Service Pack 3, compressed information store database files of 128 MB or smaller are automatically decompressed. When database files grow to larger than 128 MB, the database does not mount and the error messages are generated in the application log. Exchange 2000 Server Service Pack 3 prevents compressed databases larger than 128 MB from mounting.

  1. Right-click the folder where you want to turn off file compression, and click Properties.

  2. On the General tab, click Advanced.

  3. In the Advanced Attributes dialog box, clear the Compress contents to save disk space check box, and then click OK.

  1. Open Exchange System Manager.

  2. Expand Administrative Groups, expand your administrative group, expand Servers, right-click your storage group, and then click Properties.

  3. On theGeneral tab, under Transaction log location, click Browse.

  4. Enter the path to the new location for the log files, and then click OK.

  5. Click OK.

  1. Follow the guidance in the core Exchange Server 2007 documentation, "How to Set or Change the Location of Storage Group Log Files" (http://go.microsoft.com/fwlink/?LinkId=80702).

For more information about moving log files on Exchange Server 2003, see the Microsoft Knowledge Base article 821915, "How to Move Exchange Databases and Logs in Exchange Server 2003" (http://go.microsoft.com/fwlink/?LinkId=3052&kbid=821915).

For more information about moving log files on Exchange 2000 Server, see the Knowledge Base article 239944, "How to Move the Transaction or System Logs to Another Location" (http://go.microsoft.com/fwlink/?LinkId=3052&kbid=239944).

 
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