Microsoft KB Archive/169608

= Occasional File Corruption When Using Unbuffered I/O =

Article ID: 169608

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Server 4.0, Terminal Server Edition
 * Microsoft Windows NT Workstation 3.51
 * Microsoft Windows NT Workstation 4.0 Developer Edition
 * Microsoft Windows NT Server 3.51
 * Microsoft Windows NT Server 4.0 Standard Edition

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This article was previously published under Q169608



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, click the following article number to view the article in the Microsoft Knowledge Base:

152734 How to Obtain the Latest Windows NT 4.0 Service Pack



STATUS
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.

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.

Keywords: kbbug kbenv kbfix KB169608

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