Occasional File Corruption When Using Unbuffered I/O

 Last reviewed: October 7, 1997
Article ID: Q169608
The information in this article applies to:
  • Microsoft Windows NT Workstation versions 3.51 and 4.0
  • Microsoft Windows NT Server versions 3.51 and 4.0

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.

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.

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          : ntfilesys NTSrvWkst kbenv
Version           : WinNT:3.51,4.0
Platform          : winnt

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Last reviewed: October 7, 1997
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