Exchange database files are being 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]  

Topic Last Modified: 2011-02-24

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

On a computer that is running Microsoft Exchange 2000 Server or Microsoft Exchange Server 2003, the information store databases are written to the following default location:

<drive>:\Program Files\Exchsrvr\mdbdata

On a computer that is running Microsoft Exchange Server 2007, the database files are written to the following default location:

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

On a computer that is running Microsoft Exchange Server 2010, the database files are written to the following default location:

<drive>:\Program Files\Microsoft\Exchange Server\V14\Mailbox

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), the store may fail to mount or it may become corrupted.

The Exchange data files include the following files:

  • .edb files

  • .stm files

  • .log files

  • .dat files

  • .eml files

  • .chk files

Files that are managed by the 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 the compression of files invalidates sector independence. Compression should not be turned on for volumes that host ESE databases or any other database that uses write-ahead logging.

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

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

To turn off file compression on a given folder

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

  2. On the General tab, click Advanced.

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

To move the database files in Exchange 2000 Server or in Exchange Server 2003

  1. Open Exchange System Manager.

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

  3. On the Database tab, under Exchange database or under Exchange streaming database, click Browse, type the path location to a folder on which compression is not enabled, and then click OK.

  4. Click OK or Apply to apply your changes, and then click Yes on the warning message.

  5. After you click Yes, the stores (databases) are dismounted, moved, and then remounted. When these procedures are successfully completed, you receive the following informational message: The database files have been moved successfully.

To move the location of Exchange storage group database files in Exchange Server 2007

  1. Follow the guidance in the core Exchange Server 2007 documentation, How to Move a Storage Group Path.

To move the location of Exchange database files in Exchange Server 2010

  1. Follow the guidance in the core Exchange Server 2010 documentation, Move the Database Path.

For more information about .stm and .edb files, see Microsoft Knowledge Base article 232323, Native Content Storage in Microsoft Exchange.