You experience a nonpaged pool memory leak when you unmap and then remap Microsoft MPIO-based logical unit number to a Windows Server 2008-based computer

Consider the following scenario:

• You are running a Windows Server 2008-based computer.
• You expose to the computer an MPIO-based logical unit number (LUN) that is using the Microsoft Multipath I/O (MPIO) solution.
• You unmap the LUN from the computer, and then you remap the LUN to the same computer.

When you use the Microsoft Device Specific Module (DSM) that plugs into the MPIO in this scenario, you experience a nonpaged pool memory leak.

This issue occurs because the MPIO structures are not freed after the LUN performs the disconnect and delete operations that are associated with the unmapping and remapping process.

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 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.

Prerequisites

To apply this hotfix, you must have Windows Server 2008 installed.

Important Any existing LUNs that are claimed by the DSM may become orphaned after you apply this hotfix. To resolve the issue, follow these steps:

1. Before you apply the hotfix, export the following registry key to a .reg file:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSDSM\Parameters
2. After the hotfix has been applied, import the .reg file to the computer.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

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 Server 2008, x86 version

Windows Server 2008, x64 version

Windows Server 2008, IA-64 version

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