In Windows Server 2008 and in Windows Vista Service Pack 1 (SP1), applications or services that call the CVdsService::Reenumerate function to rescan logical unit number (LUN) objects may receive incorrect results.

For example, an application breaks a LUN object mirror, masks one plex, and then unmasks the plex to another computer. After the application performs the unmasking action, the application calls the CVdsService::Reenumerate function to rescan LUN objects. Because of this issue, the plex does not appear on the expected computer, and an exception occurs.

If the storport and SCSIport drivers receive two LUN object rescan calls within 30 seconds, the drivers skip the second rescan call. When the rescan call is skipped, the problem that is mentioned in the "Symptoms" section may occur.

To resolve this problem, install the following hotfix. This hotfix adds a delay of 45 seconds in the CVdsService::Reenumerate function to make sure that each re-enumeration call triggers a storage rescan.

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.

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 on a Windows Server 2008-based computer, no prerequisites are required.

To apply this hotfix on a Windows Vista-based computer, you must have Windows Vista SP1 installed. For more information about Windows Vista service packs, click the following article number to view the article in the Microsoft Knowledge Base:

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 Vista and Windows Server 2008 file information notes

The MANIFEST (.manifest) files and MUM (.mum) files that are installed for each environment are listed separately. MUM and MANIFEST files and their associated security catalog (.cat) files are critical to maintaining the state of the updated component. The security catalog files are signed with a Microsoft digital signature. The attributes of these files are not listed.

All supported x86-based versions of Windows Server 2008 and of Windows Vista

All supported x64-based versions of Windows Server 2008 and of Windows Vista

All supported IA-64-based versions of Windows Server 2008

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

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: Some applications that require Virtual Disk Service (VDS) calls to be completed quickly may be severely affected by this 45-second delay. To work around this issue, you can modify the appropriate registry entry to disable the delay. To do this, follow these steps:

1. Click Start, type regedit in the Start search box, and then press ENTER.
   
   If you are prompted for an administrator password or for confirmation, type the password, or provide confirmation.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VDS
3. On the Edit menu, point to New, and then click DWORD (32-bit) Value.
4. Type DisableReenumDelay, and then press ENTER.
5. Right-click DisableReenumDelay, and then click Modify.
6. In the Value data box, type 1, and then click OK.
7. Exit Registry Editor.

The value of the registry entry is read when the service is loaded. Therefore, you must restart VDS to make the value active.

You cannot disable the delay on a per-application basis. You can disable the delay only system-wide. After you disable the delay, disk changes may not be found by re-enumerate calls. Therefore, applications that rely on VDS notifications to find new disks may not receive these notifications. Some applications may not work correctly if they do not receive notifications of disk arrivals or of disk removals. Therefore, if this is a concern for you, make sure that you do not disable the delay.

If an application can recognize the disks that are supposed to be available, the application may be able to work around these lost notifications by verifying whether a disk is detected. For example, when an application masks or unmasks a LUN object, the application may recognize the disks that should be available. Therefore, we recommend that you use this hotfix only when the following conditions are true:

• The applications that use VDS can work around the lost notifications.
• No other applications use VDS to find disk arrivals and disk removals.

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base: For more information about LUN objects, visit the following Microsoft Developer Network (MSDN) Web site:

Additional file information for Windows Server 2008 and for Windows Vista

Additional files for all supported x86-based versions of Windows Server 2008 and of Windows Vista

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

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