Microsoft KB Archive/913568

= Decreased performance, driver load failures, or system instability may occur on Hot Add Memory systems that are running Windows Server 2003 =

Article ID: 913568

Article Last Modified on 2/15/2006

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APPLIES TO


 * Microsoft Windows Server 2003, Datacenter Edition (32-bit x86)
 * Microsoft Windows Server 2003, Enterprise Edition (32-bit x86)

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Important This article contains information about how to modify the registry. Make sure to back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows registry



SYMPTOMS
You may experience any one of the following problems on a Microsoft Windows Server 2003-based computer that has the Hot Add Memory feature enabled:
 * Devices do not initialize or do not work correctly.
 * Drivers do not load, or services do not start.
 * Programs fail or do not start. These programs may include Microsoft Exchange Server or Microsoft SQL Server Analysis Services.
 * System performance is poor.
 * The system is unstable.
 * The system does not start.
 * You receive errors that indicate insufficient resources.
 * You receive Stop errors.

Note By default, the Hot Add Memory feature may be enabled on the computer.



CAUSE
When the Hot Add Memory feature is enabled, the operating system pre-allocates kernel resources to handle any future memory that may be added to the computer. Kernel resources are allocated based on the capabilities of the computer instead of on the RAM that is actually installed. The kernel may allocate significant resources to RAM that may never be installed. Therefore, the Hot Add Memory feature may cause the maximum size of the paged pool to be much smaller than expected.

The problem may be most likely to occur on a computer that is running an x86-based version of Windows Server 2003 when one of the following scenarios is true:
 * The system reports that lots of RAM is supported. For example, the problem may be most likely to affect a Windows Server 2003, Datacenter Edition-based computer that supports 128 gigabytes (GB) of RAM. The Static Resource Affinity Table (SRAT) tells the operating system where RAM may be added.
 * The system uses the /3GB switch in the Boot.ini file. When this method of virtual address space allocation is used, available kernel resources are significantly reduced. Additionally, System Page Table Entry allocations may be reduced to levels that can cause performance issues.



WORKAROUND
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 your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

To work around this problem, use one of the following methods.

Method 1: Use the DynamicMemory registry parameter to limit the amount of Hot Add Memory
To set the DynamicMemory registry parameter on computers that run Windows Server 2003 with Service Pack 1 (SP1) or later versions, follow these steps:  Click Start, click Run, type regedit, and then click OK. Locate and then right-click the following registry subkey:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management

 On the Edit menu, point to New, and then click DWORD Value. Type DynamicMemory for the name of the DWORD, and then press ENTER. Right-click DynamicMemory, and then click Modify. In the Value data box, type the value that you want to use, and then click OK.

The value of this parameter is in gigabytes (GB). For example, if you set the value to 1, the kernel reserves space for a total of 1 GB of system memory or for the total amount of physical memory that is installed at startup time, whichever is larger.</li> Exit Registry Editor, and then restart the computer.</li></ol>

Method 2: Disable the Hot Add Memory feature
To disable the Hot Add Memory feature, use one of the following methods: <ul> Method A: Contact your hardware vendor to determine whether the Hot Add Memory feature can be disabled by using the BIOS. If the feature can be disabled by using the BIOS, use this method.</li> Method B: If the Hot Memory Add feature cannot be disabled by using the BIOS, we recommend that you upgrade to Windows Server 2003 SP1, and then use Method 1.

If you cannot upgrade to Windows Server 2003 SP1, you can set the /NOPAE switch in the Boot.ini file to disable Physical Address Extension (PAE) mode.

Note We do not recommend that you disable PAE mode on computers that run Windows Server 2003 with SP1 or later versions. This configuration may unintentionally disable new features that include Data Execution Prevention (DEP) support. Set the /NOPAE switch only on computers that run a version of Windows Server 2003 before SP1.

For more information about how to set the /NOPAE switch, visit the following Microsoft Web site:

http://www.microsoft.com/technet/prodtechnol/exchange/Analyzer/2b0d4c6e-92b7-410b-876b-367c4043b1c7.mspx

</li></ul>

<div class="status_section">

STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.

<div class="moreinformation_section">

MORE INFORMATION
For more information about support for the Hot Add Memory feature in Windows Server 2003, visit the following Microsoft Web site:

http://go.microsoft.com/fwlink/?linkid=57183

Keywords: kbtshoot kbexpertiseinter KB913568

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