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:
multi(0)disk(0)rdisk(0)partition(2)\WINNT="Microsoft Windows 2000 Advanced Server" /fastdetect /3GB
Some of the lines above have been wrapped for readability.
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.
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:
Information on application use of 4GT RAM Tuning
Enabling 4GT RAM Tuning when you use Windows NT Server Enterprise Edition
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
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.