MTA data 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: 2005-11-18

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 message transfer agent (MTA) data path. If the Exchange Server Analyzer determines that the value for the Compressed key is True, an error is displayed.

Microsoft does not support the storage of Exchange data files on an NTFS file system compressed volume. When you store your Exchange data files on a compressed volume, the additional overhead significantly affects Exchange performance. Additionally, after an Exchange store database reaches a certain size, approximately 4 gigabytes (GB), it may not always mount or it may become corrupted.

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. 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 Exchange store databases were able to mount. However, corruption can result in any Exchange 2000 Exchange store databases or logs that have been compressed using NTFS compression.

With Exchange 2000 Server Service Pack 3, compressed information store database files of 128 megabytes (MB) or fewer 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 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, clear the Compress contents to save disk space check box, and then click OK.

  1. On Exchange Server version 5.5, you can move the MTA database files using the Performance Optimizer tool. For more information about how to do this on Exchange 2000 Server or Exchange Server 2003, see the Microsoft Knowledge Base article 259896, "XCON: How to Change the Location of the MTA Database and Run Directory" (

For more information about Exchange data files and NTFS compression, see the following Microsoft Knowledge Base articles: