Cache Manager May Cause Data Corruption on SMB Servers on FAT

• Microsoft Windows NT Workstation version 4.0
• Microsoft Windows NT Server version 4.0

SYMPTOMS

You may encounter corrupt 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.

CAUSE

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: Q168513
        TITLE     : Windows NT Installable File System Kit (IFS) Description
  
     NOTE: Windows NT 4.0 does not include any file system filter drivers.
  
  

RESOLUTION

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 following fix or wait for the next Windows NT service pack.

This fix should have the following time stamp:

   06/27/97  06:35p               934,208 Ntkrnlmp.exe (Intel)
   06/27/97  06:34p               914,816 Ntoskrnl.exe (Intel)

   06/27/97  05:34p             1,393,600 Ntkrnlmp.exe (Alpha)
   06/27/97  05:34p             1,366,144 Ntoskrnl.exe (Alpha)

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.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. A supported fix is now available, but has not been fully regression-tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.