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

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
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).
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.

Service pack information

To resolve this problem, obtain the latest service pack for Windows Vista. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
935791 How to obtain the latest Windows Vista service pack

Hotfix information

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.

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.


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:
  1. Click Start, type regedit in the Start Search box, and then press ENTER.
  2. Locate and then click the following registry subkey:
  3. On the Edit menu, point to New, and then click DWORD Value.
  4. Type MaxMpxCt, and then press ENTER.
  5. Right-click MaxMpxCt, and then click Modify.
  6. 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.
  7. Exit Registry Editor.

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, 32-bit versions
File nameFile versionFile sizeDateTimePlatform
Update.mumNot applicable2,44923-May-200714:21Not applicable
X86_0eff413cdf04672e2f44fa972dad413c_31bf3856ad364e35_6.0.6000.20603_none_647dc4ac50e1f375.manifestNot applicable69723-May-200714:21Not applicable
X86_eeac48e6eab426417e839bddcc03b81b_31bf3856ad364e35_6.0.6000.20603_none_2b2632e4f8a9474c.manifestNot applicable70023-May-200714:21Not applicable
X86_microsoft-windows-smbserver-v1_31bf3856ad364e35_6.0.6000.20603_none_d89dc6781267f58c.manifestNot applicable4,92923-May-200714:23Not applicable
X86_microsoft-windows-smbserver_31bf3856ad364e35_6.0.6000.20603_none_f79b461606cfdb48.manifestNot applicable57,53523-May-200714:23Not applicable
Smbserver-ppdlic.xrm-msNot applicable3,13122-May-200716:06Not applicable
Windows Vista, 64-bit versions
File nameFile versionFile sizeDateTimePlatform
Amd64_3e38cd74a229847467a7cc88a7029aae_31bf3856ad364e35_6.0.6000.20603_none_66a60fa701a070b5.manifestNot applicable70123-May-200714:21Not applicable
Amd64_bc1e6a8a7abdd81dd99d59d04e8e2895_31bf3856ad364e35_6.0.6000.20603_none_86910b32ad4dca86.manifestNot applicable70423-May-200714:21Not applicable
Amd64_microsoft-windows-smbserver-v1_31bf3856ad364e35_6.0.6000.20603_none_34bc61fbcac566c2.manifestNot applicable5,19623-May-200714:28Not applicable
Amd64_microsoft-windows-smbserver_31bf3856ad364e35_6.0.6000.20603_none_53b9e199bf2d4c7e.manifestNot applicable57,57123-May-200714:28Not applicable
Update.mumNot applicable2,46323-May-200714:21Not applicable
Smbserver-ppdlic.xrm-msNot applicable3,13122-May-200711:48Not applicable
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section. This problem was first corrected in Windows Vista Service Pack 1.
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
SMB1 NotifyChange ChangeNotify

Article ID: 937082 - Last Review: 10/08/2011 17:31:00 - Revision: 4.0

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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