Microsoft KB Archive/123819

= File Manager I/O Optimizations Slow other File Transfers =

Article ID: 123819

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Advanced Server 3.1
 * Microsoft Windows NT Server 3.5
 * Microsoft Windows NT Server 3.51
 * Microsoft Windows NT Advanced Server 3.1

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This article was previously published under Q123819



SYMPTOMS
The file I/O optimizations in Windows NT File Manager can cause other processes' calls to Raw Write and Raw Read to fail.



RESOLUTION
To correct This problem:

 Always use File Manager to copy or write files. File Manager will cancel the NTNotifyDirectoryChange SMB before submitting the RAW read/write operation. Modify the Windows NT Registry as follows:

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

 Run Registry Editor (REGEDT32.EXE). From the \HKEY_CURRENT_USER subtree, go to the following key:

\Software\Microsoft\FileManager\Settings

 From the Edit menu, choose Add Value. Enter the following:

Value Name: ChangeNotifyTime

Data Type: REG_SZ

String: 0 (disable; 1 for enable)

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MORE INFORMATION
Normal CORE mode read and write operations occur in approximately 8K units. For each 8K the redirector must submit a new SMB (server message block). As an optimization, Microsoft networks can use RAW mode to send data in 64K units, requiring one SMB for every 64K. The transport subdivides this buffer as needed. One stipulation of RAW mode is that the Virtual Circuit must be tied up while the operation is in progress because the data frames contain no SMB information to correlate it. No other SMB can be allowed during this time.

Windows NT introduced a new SMB called NTNotifyDirectoryChange. This causes the server to notify the client if directory information changes. For example, if another client adds a file to a directory, Windows NT File Manager uses NTNotifyDirectoryChange.

This SMB is classified as a long term request. The SMB is received by the server but is not returned until a change occurs (or until the SMB is canceled by the client). Because the client does not know when the server will complete the SMB, it cannot tie up the virtual circuit. Therefore, the client does not use RAW mode when an NTNotifyDirectoryChange is pending.

When necessary, File Manager cancels the request to take advantage of RAW mode. However, other processes such as NTVDM or SETUP are not aware that RAW mode has been disabled.

Additional query words: prodnt 3.10 smb pending

Keywords: KB123819

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