Exchange 2000 requires /3GB switch with more than 1 gigabyte of physical RAM (266096)

SUMMARY

You must change the overall memory allocation on a computer that runs Microsoft Exchange 2000 Server when all the following conditions are true:

The computer contains 1 gigabyte (GB) or more of physical random access memory (RAM).
The computer is home to mailboxes or to public folders.

You do not have to make changes if the computer does not have any mailboxes or public folders on it (such as a mail gateway).

After you have installed Windows 2000 Advanced Server, you must modify the Boot.ini file and add the /3GB parameter to the startup line. For example:

[Boot Loader]
Timeout=30
Default=multi(0)disk(0)rdisk(0)partition(2)\WINNT
[Operating Systems]
multi(0)disk(0)rdisk(0)partition(2)\WINNT="Microsoft Windows 2000 Advanced Server" /fastdetect /3GB

Note Some of the lines above have been wrapped for readability.

Note Do not add the /3GB switch if you are running Windows 2000 Server, Microsoft Small Business Server 2000, or Microsoft BackOffice Server 2000. If the /3GB switch has been added to the Boot.ini file on these operating systems, it must be removed because it can contribute to virtual memory fragmentation on these systems. This switch is designed for use only with Windows 2000 Advanced Server and later.

MORE INFORMATION

By default, Windows 2000 Advanced Server reserves 2 GB of virtual address space for the kernel, and allows user mode processes (such as the Exchange 2000 information store process, Store.exe) to use 2 GB of virtual address space. Virtual address space for a specific process is allocated at Startup and increases as more memory is used during run-time. It is normal for the actual memory usage (working set) of a process to be much less than the address space the process was allocated. On an Exchange 2000 server that has more than 1 gigabyte of memory and that is home to mailboxes or public folders, you must modify Windows 2000 Advanced Server so that 3 gigabytes are available for user mode applications. For additional information about this /3GB setting, click the following article numbers to view the articles in the Microsoft Knowledge Base:

171793 Information on application use of 4GT RAM Tuning

189293 Enabling 4GT RAM Tuning when you use Windows NT Server Enterprise Edition

Note It is very important that the Store.exe process does not run out of virtual address space. When this happens, memory allocations fail (even if there is plenty of physical RAM left) and you must restart the Microsoft Exchange Information Store service.

For example, a server with 2 GB of physical RAM without the /3GB switch in the Boot.ini file will run out of memory when the Store.exe virtual address space reaches 2 GB. Windows Task Manager shows that only about 1.5 GB is actually being used but the server will be out of memory nonetheless.

You may also monitor the virtual address consumption with Performance Monitoring. Add the Virtual Bytes counter for the Store.exe process to ensure an accurate reading of the virtual space. The Store.exe process is the only Exchange 2000 process that you need to monitor; other Exchange 2000 processes will not grow large enough to cause any problems.