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Q169608: Occasional File Corruption When Using Unbuffered I/O

Article: Q169608
Product(s): Microsoft Windows NT
Version(s): winnt:3.51,4.0
Operating System(s): 
Keyword(s): kbenv kbWinNT400sp4fix
Last Modified: 10-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Workstation versions 3.51, 4.0 
- Microsoft Windows NT Server versions 3.51, 4.0 
- Microsoft Windows NT Server version 4.0, Terminal Server Edition 
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SYMPTOMS
========

File data may be read incorrectly, or disk files may be corrupted by
applications that use a combination of buffered and unbuffered I/O to access the
files.

In particular, if the following sequence is executed repeatedly, data corruption
can sometimes be observed in under an hour:

1. Open the file cached.

2. Completely write the file with data.

3. Close the file.

4. Open the file non-cached.

5. Read back the data.

The problem described here is exhibited with both FAT and NTFS volumes on Windows
NT 3.51 systems, but only on FAT volumes on Windows NT 4.0 systems.

CAUSE
=====

When a file is opened for non-cached access, Windows NT tries to tear down the
cache map for the file, provided there are no other processes that have the file
open in a cached mode. This is done to avoid subsequent cache coherency
overhead. The problem described here comes about because Windows NT fails to
correctly take into account the fact that the lazy writer might still be
operating on the file and might need some of the data structures being
deallocated. Therefore this problem is not likely to be encountered except in
situations where the non-cached read is performed immediately following the
cached write.

RESOLUTION
==========

To resolve this problem, obtain the latest service pack for Windows NT 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,
please see the following article in the Microsoft Knowledge Base:

  Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack


STATUS
======

Microsoft has confirmed this to be 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.


Microsoft has confirmed this to be a problem in Windows NT version 3.51.

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.



Additional query words:

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Keywords          : kbenv kbWinNT400sp4fix 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT400search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbNTTermServ400 kbNTTermServSearch kbWinNTS351search
Version           : winnt:3.51,4.0
Issue type        : kbbug
Solution Type     : kbfix

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