Occasional File Corruption When Using Unbuffered I/O

ID: Q169608

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

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:

Open the file cached.

Completely write the file with data.

Close the file.

Open the file non-cached.

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.

Keywords : kbenv NT4SP4Fix kbbug4.00 kbfix4.00.sp2 ntfilesys NTSrvWkst
Version : WinNT:3.51,4.0
Platform : winnt
Issue type : kbbug