Cache Manager May Cause Data Corruption on SMB Servers on FAT

You may encounter corrupted files if Windows NT is installed on a FAT partition or shared CDFS volume that has a file system filter driver running on that volume.

This problem is caused by Memory Descriptor List (MDL) interactions between the Cache Manager, the SMB server, the file system filter driver, and FAT. There is an error in the Windows NT Cache Manager that may cause data corruption when the following conditions are true:

• Windows NT file server (Srv.sys) is running and sharing data on a local FAT-based file system (Fastfat.sys).
  
  NOTE: This problem does not occur if the server is sharing data on NTFS systems. However, the problem may exist with other third-party file systems or other code that exercises MDL I/O in ways similar to Srv.sys.
• Windows NT is using a file system filter driver. The filter driver must be aware of the Fast MDL routines and it must filter I/O on the FAT-based file system.
  
  For more information on file system filter drivers, please see the following article in the Microsoft Knowledge Base:
  
  ARTICLE-ID: 168513  (http://support.microsoft.com/kb/168513/EN-US/ )
  TITLE : Windows NT Installable File System Kit (IFS) Description
  
  NOTE: Windows NT 4.0 does not include any file system filter drivers.

For example, when a filter driver filters data I/O on an SMB server, which is shared on a FAT file system, the I/O requests that flow from the network system through the server, to the filter driver, and into the FAT partition may cause data corruption.

An updated version of the Windows NT kernel (which includes Cache Manager) no longer ignores returns from the filter driver that indicate the filter did not write the data or free the MDL. Cache Manager now takes system- defined default actions.

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
For your convenience, the English version of this post-SP3 hotfix has been posted to the following Internet location. However, Microsoft recommends that you install Windows NT 4.0 Service Pack 4 to correct this problem.


NOTE: Service Pack 3 must be applied to Windows NT 4.0 prior to applying this fix.

Mdl-fix has been superseded by Getadmin-fix. You can find the original hotfix at the following Microsoft ftp site:

You can work around this problem by using NTFS partitions for SMB server-based shares instead of FAT partitions or by not using any file system filter drivers that filter I/O on top of FAT-based server volumes.

Microsoft has confirmed that this is a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.