Multipath I/O disks may disappear after you use the Hot Add Processor feature to add a new CPU to a Windows Server 2008-based computer

Consider the following scenario:

• Windows Server 2008 is running on a computer that supports the Hot Add Processor feature.
• The computer uses multipath I/O (MPIO) disks.
• You use the Hot Add Processor feature to add a new CPU to the computer, or you use the PnpCPU.exe tool to simulate hot addition of a new CPU.

In this scenario, the MPIO disks may disappear from the system.

This problem occurs because the status of the MPIO disks is not updated as expected during plug-and-play resource rebalance.

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

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.

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, 32-bit editions

Windows Server 2008, 64-bit editions

Windows Server 2008, Itanium-based versions

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

PnpCPU.exe is a command-line tool that simulates the hot addition of processors to a running instance of Windows Server 2008. This tool is included in the Windows Driver Kit (WDK). For more information, visit the following Microsoft Web site:For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: