Exchange 2003 Memory Configuration change for Windows 2003 (PAE Support)

Posted by bink on July 6 2005, 6:10 PM. Posted in Exchange.

There has been significant change to Exchange 2003’s recommended Boot.ini configuration settings.The following change has been made to Microsoft Exchange 2003 Support Policy.

It is recommended and supported to run Exchange 2003 with the PAE (Physical Address Extension) kernel on Windows 2003: Due to the issue ( Hotfix in article 834628 )found in Windows 2003 RTM running the PAE kernel , the fact that Exchange does not take advantage of more than 4GB of memory and the fact that Exchange running on PAE kernels was not initially tested; the Exchange Product group originally recommended running the /NOPAE switch in the boot.ini to preventthe PAE kernel from loading.This decision has been reversed for the following reasons:

a.       Windows 2003 SP1 was released: <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /?> <o:p> </o:p>

·         Windows 2003 Sp1 contains the fix for 834628 so Exchange 2003 is stable running on the PAE kernel.<o:p></o:p>

·         Windows 2003 SP1 contains new security features ( Data Execution Prevention (DEP )) which require the PAE kernel.Exchange 2003 needs to support PAE to take advantage of these new security features.Windows 2003 SP1 will automatically set DEP specific boot.ini settings to take advantage of DEP capable hardware.<o:p></o:p>

b.      New PCI-Express based server chipsets require PAE to take advantage of all the memory installed on a system (4GB) :<o:p></o:p>

Some of the physical address space on server systems is used to provide memory mapping of IO resources on the system chipset. This memory mapped IO (MMIO) space is typically provided below the 4GB address boundary. In a system with 4GB of physical memory this MMIO space pushes a section of physical memory above the 4GB address boundary. If the software running on the server supports only 32-bit physical addressing, it will not look for memory over the 4GB boundary. This results in the OS not providing access to all 4GB of physical memory. The amount of ‘hidden’ memory is equal to the address space taken up by the MMIO. PCI Express confounds this problem by providing extended PCI configuration space to support such features as Advanced Error Reporting (AER). This means the size of MMIO space required to map the chipset IO resources gets larger. Some early PCI Express chipsets confound the issue further by providing coarse granularity for this mapping which results in a range of 512MB being carved out for MMIO. This results in customers reporting hidden memory of 512MB to 768MB on servers using such chipsets.<o:p></o:p>

c.The Exchange Product Group tested Exchange 2003 SP1/SP2 on Windows 2003 (/w 834628 ) with the PAE kernel and on Windows 2003 SP1 with PAE and DEP enabled:<o:p></o:p>

·         The Exchange Product Group did not find any issues relating to running on the PAE kernel nor running with DEP enabled (software and hardware enabled).

Additional Resources/Questions

  1. How can the boot.ini configuration be validated in a running environment? Use the Exchange Best Practices Analyzer Tool The tool has been updated to include the support policy change outlined in this Flash. <o:p> </o:p>
  2. How should Exchange 2003 memory based performance issues be troubleshooted? Use the Troubleshooting Exchange Server 2003 Performance whitepaper.<o:p></o:p>
  3. What is Microsoft’s stance on running Exchange on Windows 2000 with PAE? It is supported but not recommended. Hotfix 838647 is required for support.Windows 2000 does not have the security features that require PAE so the only benefit of running PAE on Windows 2000 for Exchange is to enable all memory access on newer PCI-Express based servers.It is not a well tested scenario so it is not recommended.

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