DFS Replication does not use Remote Differential Compression (RDC) when replicating very large files on a computer that is running Windows Server 2008 R2

Consider the following scenario:

• You install the Distributed File System (DFS) Replication service under the File Services role on some computers that are running Windows Server 2008 R2.
• You configure one or more replicated folders between these computers by using the DFS Management Microsoft Management Console (MMC) snap-in.
• These replication folders contain some large files such as a virtual hard disk (VHD).
• These files are changed on one of the computers after the files have replicated out.

In this scenario, the DFS Replication service does not use the Remote Differential Compression algorithm to replicate the changes that are in the large files to the replication partners. Instead, the whole file is replicated to the receiving members that are in the replication group. Therefore, the wide area network (WAN) bandwidth is unnecessarily consumed if this data is replicated between remote sites over WAN links. However, the expected behavior is that only the changes to the file are replicated by the DFS Replication service and that the Remote Differential Compression algorithm is used.

Note

• This issue only applies to very large files such as VHDs.
• In some instances, nothing is downloaded to the replication partners when some changes occur to these large files.

For very large files, the DFS Replication service incorrectly marks a file download operation as finished before the file is completely downloaded. Therefore, the file is not replicated by using the Remote Differential Compression algorithm correctly. When the DFS Replication service notices that the whole download operation is not completely downloaded, DFS Replication that is located on the receiving member downloads the whole file from the sending member.

Hotfix information

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 the problem 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.

Prerequisites

To apply this hotfix, your computer must be running Windows Server 2008 R2. Additionally, the DFS Replication service under the File Servers role must be installed.

Installation instructions

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.

After you install this hotfix, you must create the following registry key:





Note This value of the registry key represent 4 hours in milliseconds.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

File information

The English (United States) version of this hotfix installs files that have the attributes that are listed in the following tables. The dates and the times for these files are listed in Coordinated Universal Time (UTC). The dates and the times for these files on your local computer are displayed in your local time together with your current daylight saving time (DST) bias. Additionally, the dates and the times may change when you perform certain operations on the files.

Windows Server 2008 R2 file information notes

The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed separately in the "Additional file information for Windows Server 2008 R2" section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are critical to maintaining the state of the updated component. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.

For all supported x64-based versions of Windows Server 2008 R2

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

You can use Performance Monitor to track the following Remote Differential Compression feature-related counters on the downstream members. When the issue occurs, the files are replicated. But the values of these counters are not increased.

• DFS Replicated Folders\RDC Number of Files Received
• DFS Replicated Folders\RDC Bytes Received

Additionally, the value of the following counter has a very high value:

DFS Replicated Folders\Size of Files Received

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: For more information about Remote Differential Compression, visit the following Microsoft Web site.

Additional file information

Additional file information for Windows Server 2008 R2

Additional files for all supported x64-based versions of Windows Server 2008 R2