XADM: An Exchange 2000 Server with the "/3GB" Switch in the Boot.ini File May Lose Network Connectivity Under a Heavy Messaging Load

If Exchange 2000 Server is running on a Windows 2000 Advanced Server-based computer or a Windows 2000 Datacenter Server-based computer with the /3GB switch in place (in the Boot.ini file), the computer may lose network connectivity (especially when messaging traffic is high). You may have to restart the server to restore network connectivity.

This problem may occur if the kernel uses up the Free System page table entries (PTEs) on heavily loaded servers that are configured with the /3GB switch. This results in random network problems (the server drops packets or can no longer be pinged), which may require a system restart.

To resolve this problem, you can modify the SystemPages registry value to increase the PTE pool; however, modify the SystemPages value only if you determine that the server is in a low PTE state. To determine if the server is in a low PTE state, use the following system monitor counter to track Free System PTEs: This counter is used to monitor the available PTEs on the server. Typically, an Exchange 2000 server with the /3GB switch set should show 10,000 or more free PTEs during heavy messaging stress. If this counter dips below 10,000 and you experience network problems, you can modify the SystemPages registry value to resolve the low PTE condition.

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

To modify the SystemPages value:

1. Start Registry Editor (Regedt32.exe).
2. Locate and double-click the SystemPages value under the following key in the registry:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management
3. Delete the existing value, click Decimal, type 30000, and then click OK.
   
   Important Windows 2000 Service Pack 3 (SP3) with the /3GB switch increased available Paged Pool memory to 258 megabytes (MB) at the expense of PTEs. Only 16,384 PTEs are available when you use the /3GB switch, so set the SystemPages value to 30000 to start with a greater number of PTEs. You can adjust this number up or down, depending on the available PTEs and the available paged pool memory.
4. Quit Registry Editor.

If you set this key to 30000, you increase the PTE pool by 30 MB. This 30 MB is taken from the Paged Pool Memory space. In other words, if you increase your PTE pool by 30 MB, you reduce the Paged Pool Memory by 30 MB. Reducing Paged Pool Memory may adversely affect the computer's performance, so modify the System Pages registry value only if you must.

Microsoft has confirmed that this is a problem in Microsoft Exchange 2000 Server.

If you are running Exchange 2000 on a Windows 2000 Advanced Server-based computer or a Windows 2000 Datacenter Server-based computer with more than 1 gigabyte (GB) of RAM, you must add the /3GB switch to the server's Boot.ini file. For additional information, click the article number below to view the article in the Microsoft Knowledge Base: Running Windows 2000 with the /3GB switch reduces the kernel memory that is available, for example, if Windows 2000 Server Service Pack 2 (SP2) is running on an 8-processor, 4 GB RAM computer:

• Without the /3GB switch:
  Non-paged Pool Memory Max (KB) =280,580
  Paged Pool Memory Max (KB) =339,968
  Free System PTEs (KB) =446,064
• With the /3GB switch:
  Non-paged Pool Memory Max (KB) =149,508
  Paged Pool Memory Max (KB) =262,144
  Free System PTEs (KB) =61,880

NOTE: The numbers are specific to the hardware (for example, the number of processors and the amount of memory). The data in this article was taken by using a kernel debugger memory dump file and is measured in kilobytes.