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This article discusses a problem that occurs when network users access files on a computer that is running Microsoft Windows XP Professional when the computer is being used as a file server.
By default, there is a restriction that prohibits more than 10 concurrent server message block (SMB) commands in the Windows XP Professional Server service. This restriction also applies to other Windows client computer operating systems. For example, an SMB command occurs when a call is made to open a file. Most SMB commands are processed immediately. For example, the file open command is processed immediately. Therefore, a maximum of 10 concurrent commands is typically not a problem.
However, there are some SMB commands that are named "long-term SMB requests." These long-term SMB requests remain open until they are answered. Typically, after an answer is received, another command of the same type is sent immediately.
Additionally, a long-term SMB request is a change notification. For example, if you open Windows Explorer, and then you click a specific folder on the network, a change notification is sent to the computer that hosts the folder. This occurs whenever something changes in this folder. Then, a change notification is sent back to the client computer so that Windows Explorer can update the window and display the new file. If a computer that is running Windows XP Professional hosts the folder, only 10 SMB commands can be used at the same time. All other requests are not answered. You may also receive an error message when the other requests try to open files over the network.
This problem occurs because of an intentional limitation in the Windows XP Professional Server service. Windows XP Professional is designed as a client computer operating system. Therefore, Windows XP Professional is not optimized for server tasks.
To resolve this problem, a hotfix is available that enables you to configure the number of concurrent SMB commands by using the MaxMpxCt registry value. This hotfix enables you to configure the MaxMpxCt value to a maximum of 255. For more information, see the "Registry information" section and the "More Information" section.
A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.
If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.
Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site:
Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.
You must install Windows XP Professional Service Pack 2 (SP2) to install this hotfix.
You must restart the Server service after you apply this hotfix. If you are prompted, restart the computer after you install the hotfix.
Hotfix replacement information
This hotfix does not replace any other hotfixes.
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
To enable this hotfix, follow these steps:
Click Start, click Run, type regedit, and then click OK.
Locate and then click to select the following registry subkey:
On the Edit menu, point to New, and then click DWORD Value.
Type MaxMpxCt, and then press ENTER.
Right-click MaxMpxCt, and then click Modify.
In the Value data box, type the desired value, and then click OK.
Note You can set the number of concurrent SMB commands to a value that is between 10 and 255. The default value is 10. In Microsoft Windows Server 2003, you can set the number of concurrent SMB commands to a maximum value of 65,535.
Close Registry Editor.
The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
The actual value of maximum concurrent SMB commands is determined by the minimum of 2 values. These values are the MaxMpxCt value on the server side and the MaxCmds registry value on the client computer. By default, the MaxCmds value is set to 50 in Windows XP Professional. You cannot set this value to more than 65,535.
On the Windows XP computer that is acting as the server, the MaxMpxCt value, the MaxWorkItems value, and the Size value are located in the following registry subkey:
You must set the following registry values on the Windows XP Professional-based computer that is acting as the file server. By doing this, you give the necessary resources to the Server service.
You must set the MaxWorkItems value to at least 4 times the MaxMpxCt value. By default, the MaxWorkItems value is set to 64 in Windows XP Professional. You can set this value to a maximum of 1,024. We recommend that you use this setting only on computers that have sufficient memory. The exact amount of memory that you must have depends on the configuration details. In this scenario, we recommend that you use at least 1 gigabyte (GB) of memory.
By default, the Size value is set to 1 in Windows XP Professional. You must set the Size value to at least 2. If you incur problems, you must set the Size value to 3.A Size value of 1 is used to optimize Windows XP Professional for local applications. A Size value of 2 is used to balance resource usage between local application and remote applications. A Size value of 3 is used to optimize Windows XP Professional for network activity.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates