This Exchange server has more than 8 processors

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at https://go.microsoft.com/fwlink/?linkid=34707.]  

Topic Last Modified: 2009-08-19

The Microsoft® Exchange Server Analyzer Tool queries the Win32_ComputerSystem Microsoft Windows® Management Instrumentation (WMI) class to determine the following:

• If the NumberOfLogicalProcessors property exists in WMI, the Exchange Server Analyzer determines the current value for NumberOfLogicalProcessors. NumberOfLogicalProcessors returns the logical processor count in the computer. This property is available in Windows Server 2008. By default, NumberOfLogicalProcessors is not available in Windows Server 2003. The hotfix that is mentioned in Microsoft Knowledge Base article 932370, "The number of physical hyperthreading-enabled processors or the number of physical multicore processors is incorrectly reported in Windows Server 2003" (https://go.microsoft.com/fwlink/?linkid=3052&kbid=932370) adds the NumberOfLogicalProcessors property to Windows Server 2003.

• If the NumberOfLogicalProcessors property does not exist, the Exchange Server Analyzer determines the current value for NumberOfProcessors. In Windows Server 2008, NumberOfProcessors only returns the number of physical processors. By default, in Windows Server 2003, NumberOfProcessors returns the number of logical processors.

If the Exchange Server Analyzer finds that the value for the number of logical processors is greater than eight, a warning is displayed. However, if this server is configured to use Intel Hyper-Threading Technology, this warning can be safely ignored. Hyper-Threading Technology enables multi-threaded software applications to run threads in parallel. Hyper-Threading Technology requires a computer system with an Intel Pentium 4 processor supporting Hyper-Threading Technology and an HT Technology-enabled chipset, BIOS, and operating system.

Exchange 2000 Server and Exchange Server 2003 can effectively use only eight processors on a computer. Specifically, the Microsoft Exchange Information Store service is optimized for a maximum on eight processors.

On computers that have more than eight processors, it is recommended that you use hardware partitioning to partition the computer into multiple eight-processor computers or into multiple four-processor computers. Alternatively, you can configure CPU affinity for the Microsoft Exchange Information Store process (Store.exe) to only eight processors.

As soon as the Microsoft Exchange Information Store process has been limited to eight processors either through CPU affinity or through hardware partitioning, it is recommended that you upgrade to the latest available service pack and Exchange update rollups. This is especially important if you are running Exchange Server 2003.

Previously, Exchange server performance has shown marginal improvements when the number of processors in back-end servers increases to more than four. With more than eight processors, the performance increase is marginal at best, and sometimes performance can decrease. The falloff in performance gain with additional processors has become more pronounced with the types of processors used on more recent computers. With Exchange Server 2003 Service Pack 1, scalability with additional processors is much improved. When hyper-threading is enabled, eight-processor servers now provide a 50 percent increase in performance over four-processor servers. Using eight-processor computers for back-end servers is now appropriate in many scenarios. Dual-processor servers are still recommended for front-end servers.

As stated, if this Exchange Server computer is using Hyper-Threading Technology, this warning can be safely ignored.

For more information about Exchange Server resource scalability, see the Microsoft Knowledge Base article 827281, "CPU and Memory Scalability for Exchange 2000 and Exchange 2003" (https://go.microsoft.com/fwlink/?linkid=3052&kbid=827281).

For more information, see also the Knowledge Base article 271088, "XGEN: Optimizing Windows 2000 Active Directory Servers with Six or Eight Processors to Run with Exchange 2000" (https://go.microsoft.com/fwlink/?linkid=3052&kbid=271088).

For more information about Hyper-Threading Technology, see the Intel Web site (http://www.intel.com/info/hyperthreading).