A differencing VHD file that is created by using Microsoft iSCSI Software Target 3.3 becomes corrupted when you mount or attach it in Windows Server 2008 R2 or in Windows 7

Consider the following scenario. You create a�differencing virtual hard disk (VHD) file by using Microsoft iSCSI Software Target 3.3. Then, you perform one of the following operations:

• You mount the differencing VHD file natively on a computer that is running Windows Server 2008 R2 or Windows 7.
• You attach the differencing VHD file to a virtual machine that is hosted on a computer that is running Windows Server 2008 R2 and that has the Hyper-V server role installed.

In this scenario, the differencing VHD file becomes corrupted.

Note�This issue does not occur when you use fixed VHD files.

This issue occurs because Microsoft iSCSI Software Target 3.3�does not use the format for sector bitmaps that�Windows 7 and Windows Server 2008 R2 use�when�Microsoft iSCSI Software Target 3.3 updates the sector bitmap of the differencing VHD file. Therefore, the differencing VHD file becomes corrupted after you mount or attach the file in Windows 7 or in Windows Server 2008 R2.

To�prevent�this issue, apply the following hotfix. This hotfix prevents you from mounting or attaching differencing VHD files.�After you apply the hotfix, you can no longer perform the following operations:

• Mount differencing VHD files that are created by Microsoft iSCSI Software Target 3.3 on a computer that is running Windows Server 2008 R2 or Windows 7.
• Attach differencing VHD files that are created by using Microsoft iSCSI Software Target 3.3 to a virtual machine. This applies to virtual machines that are hosted on a computer that is running Windows Server 2008 R2 and that has the Hyper-V server role installed.

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 website: 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, you must be running one of the following operating systems:

• Windows 7
• Windows 7 Service Pack 1 (SP1)
• Windows Server 2008 R2
• Windows Server 2008 R2 Service Pack 1 (SP1)

For more information about how to obtain a Windows 7 or Windows Server 2008 R2 service pack, click the following article number to view the article in the Microsoft Knowledge Base:

Registry information

To use the hotfix in this package, you do not have to make any changes to the registry.

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 global 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 7 and Windows Server 2008 R2 file information notes

Important Windows 7 hotfixes and Windows Server 2008 R2 hotfixes are included in the same packages. However, hotfixes on the Hotfix Request page are listed under both operating systems. To request the hotfix package that applies to one or both operating systems, select the hotfix that is listed under "Windows 7/Windows Server 2008 R2" on the page. Always refer to the "Applies To" section in articles to determine the actual operating system that each hotfix applies to.

• The files that apply to a specific product, milestone (RTM, SPn), and service branch (LDR, GDR) can be identified by examining the file version numbers as shown in the following table:

  Version	Product	Milestone	Service branch
  6.1.760 0.16xxx	Windows 7 and Windows Server 2008 R2	RTM	GDR
  6.1.760 0.21xxx	Windows 7 and Windows Server 2008 R2	RTM	LDR
  6.1.760 1.17xxx	Windows 7 and Windows Server 2008 R2	SP1	GDR
  6.1.760 1.21xxx	Windows 7 and Windows Server 2008 R2	SP1	LDR

• GDR service branches contain only those fixes that are widely released to address widespread, critical issues. LDR service branches contain hotfixes in addition to widely released fixes.
• 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 7 and 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 x86-based versions of Windows 7

For all supported x64-based versions of Windows 7 and of Windows Server 2008 R2

For all supported IA-64-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.

For more information about the virtual hard disk (VHD) format, visit the following Microsoft website:For more information about Microsoft iSCSI Software Target 3.3, visit the following Microsoft websites: For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

Additional file information

Additional file information for Windows 7 and for Windows Server 2008 R2

Additional files for all supported x86-based versions of Windows 7

Additional files for all supported x64-based versions of Windows 7 and of Windows Server 2008 R2

Additional files for all supported IA-64-based versions of Windows Server 2008 R2