Microsoft KB Archive/937082

= You cannot configure the maximum number of concurrent SMB requests that are sent to a Windows Vista-based file server =

Article ID: 937082

Article Last Modified on 8/29/2007

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APPLIES TO


 * Windows Vista Ultimate
 * Windows Vista Business
 * Windows Vista Enterprise
 * Windows Vista Ultimate 64-bit Edition
 * Windows Vista Business 64-bit Edition
 * Windows Vista Enterprise 64-bit Edition

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Important This article contains information about how to modify the registry. Make sure that you back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows registry



SYMPTOMS
You cannot configure the maximum number of concurrent SMB requests that are sent to a Windows Vista-based file server.

When a Windows Vista-based computer is used as a file server, users access files by using long-term Server Message Block (SMB) requests. By default, only 10 SMB requests can be sent to the server at the same time. All other SMB requests are not answered. Therefore, the user of a client computer may receive an error message when the user tries to access files by using long-term SMB requests.

Note Unlike typical SMB requests, a long-term SMB request remains open until it is answered by the server. A typical long-term SMB request is the NotifyChange SMB request (NT_TRANSACT_NOTIFY_CHANGE).



CAUSE
This problem occurs because the Server service in Windows Vista is intentionally limited. By default, a restriction prohibits more than 10 concurrent SMB requests to be sent to the Server service in Windows Vista. Because Windows Vista is designed as a client operating system, Windows Vista is not optimized for server tasks.

Most SMB requests are processed immediately. However, long-term SMB requests may cause a problem.



RESOLUTION
To resolve this problem, apply the following hotfix. This hotfix lets you use the MaxMpxCt registry entry to configure the maximum number of concurrent SMB requests. You can set the value of MaxMpxCt to a maximum of 255.

Hotfix information
A supported hotfix is now 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 service pack that contains this hotfix.

To resolve this problem, submit a request to Microsoft Online Customer Services to obtain the hotfix. To submit an online request to obtain the hotfix, visit the following Microsoft Web site:

http://go.microsoft.com/?linkid=6294451

Note If additional issues occur or 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. To create a separate service request, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

Prerequisites
No prerequisites are required.

Restart requirement
You must restart the computer after you apply this hotfix.

Hotfix replacement information
This hotfix does not replace any other hotfixes.

Registry information
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

To enable this hotfix, follow these steps:  Click Start, type regedit in the Start Search box, and then press ENTER. Locate and then click 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 a value, and then click OK.

Note You can set the maximum number of concurrent SMB requests to a value from 10 through 255. The default value is 10.</li> Exit Registry Editor.</li></ol>

File information
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.

Windows Vista, 64-bit versions
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STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.

<div class="moreinformation_section">

MORE INFORMATION
The maximum value of concurrent SMB requests is equal to the minimum of the following two values:
 * The value of the MaxMpxCt entry on the server
 * The value of the MaxCmds entry on the client computer

By default, the MaxCmds entry is set to 50 in Windows Vista. You cannot set this value to more than 65,535.

On a Windows Vista-based server, the MaxMpxCt entry, the MaxWorkItems entry, and the Size entry are located in the following registry subkey:

On a Windows Vista-based client computer, the MaxCmds entry is located in the following registry subkey:

You must set the following registry entries on the server.
 * Set the value of MaxWorkItems to at least four times the value of MaxMpxCt. By default, MaxWorkItems is set to 64 in Windows Vista. You can set this entry to a maximum of 1,024. We recommend that you use this setting only on a computer that has sufficient memory. If you use the maximum setting, we recommend that you use at least 1 gigabyte (GB) of memory.
 * By default, the value of the Size entry is 1 in Windows Vista. Set the Size entry to at least 2. If you experience problems, set the Size entry to 3.
 * A value of 1 optimizes Windows Vista for local applications.
 * A value of 2 balances resource usage between local application and remote applications.
 * A value of 3 optimizes Windows Vista for network activity.

Note When this article mentions the SMB protocol, the article refers to the traditional SMB protocol instead of to the SMB2 protocol. The SMB2 protocol was introduced in Windows Vista to enable faster communication between Windows Vista-based computers.

For more information about this problem in Microsoft Windows XP, click the following article number to view the article in the Microsoft Knowledge Base:

926646 You cannot increase the limit concurrent SMB command in the Windows XP Professional Server service

For more information about the terms that are used to describe software updates, 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

Additional query words: SMB1 NotifyChange ChangeNotify

Keywords: kbbug kbfix kbqfe kbpubtypekc kbexpertiseinter kbhotfixserver kbwinvistapostrtmfix KB937082

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