You encounter poor performance when you use the SMB 2.0 protocol to perform network-related operations, such as ADMT migration, on computers that are running Windows Server 2008 or Windows Vista

You encounter poor performance on a computer that is running Windows Server 2008 or Windows Vista when you perform network-related operations. These network-related operations include when you copy a shared file, move a shared file, or use the Active Directory Migration Tool (ADMT).

For example, the source or destination domain controller is running Windows Server 2008. In this example, an ADMT migration takes three times longer than a migration between two domain controllers that are running versions pre-Windows Server 2008.

In another example, both the source and destination domain controllers are running Windows Server 2008. In this example, an ADMT migration takes six times longer than a migration between two domain controllers that are both running versions pre-Windows Server 2008.

Network-related operations in Windows Vista and in Windows Server 2008 are based on Server Message Block (SMB) 2.0. When an SMB 2.0 server receives a request that will take a long time to process, the server processes the request differently. In this case, the server sends an interim response to the client, and then the server switches to processing the request asynchronously. However, the SMB 2.0 server waits synchronously for TCP to deliver this interim response. This behavior may produce a 200-millisecond delay because of the ACK response interval of TCP. Therefore, this delay causes the poor performance mentioned in the "Symptoms" section.

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem is that described in this article. Apply this hotfix only to systems that are experiencing the problem is described in this article. 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.


Important Windows Vista and Windows Server 2008 hotfixes are included in the same packages. However, only one of these products may be listed on the �Hotfix Request� page. To request the hotfix package that applies to both Windows Vista and Windows Server 2008, just select the product that is listed on the page.

Prerequisites

To apply this hotfix, your computer must be running one of the following operating systems:

• Windows Vista Service Pack 1 (SP1)
• Windows Server 2008

Restart requirement

You must restart the computer after you apply this hotfix.

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.

For all supported x86-based versions of Windows Vista and of Windows Server 2008

For all supported x64-based versions of Windows Vista and of Windows Server 2008

For all supported Itanium-based versions of Windows Server 2008

To work around this issue, disable SMB 2.0. To do this, follow these steps:

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:

1. Click Start, type regedit in the Start Search box, and then press ENTER.
2. Locate and then click the following registry subkey:
   
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type SMB2, and then press ENTER.
5. On the Edit menu, click Modify.
6. Type 0 (zero), and then click OK.
7. Exit Registry Editor.
8. Restart the computer.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

For more information about the new networking features in Windows Server 2008 and in Windows Vista, such as SMB 2.0, visit the following Microsoft Web site: For more information, click the following article number to view the article in the Microsoft Knowledge Base: