Here is a great article that gives a good introduction to how to set the correct Page File Sizes in Microsoft Windows Server 2008 R2.

The 64-bit versions of Microsoft Windows Server 2008 and Microsoft Windows Server 2008 R2 can support more RAM than the 32-bit versions of Windows Server. When lots of memory is added to a computer, a paging file may not be required. When you use the Memory-Pages/sec counter to measure paging file use, the value that is returned may not be accurate. To obtain an accurate measurement of paging file use, you must also use other performance counters. You can use System Monitor measurements to calculate the size of the paging file that your computer requires.

Windows Server 2008 and Windows Server 2008 R2 Domain Controllers are not supported without a configured pagefile. Because the algorithm the LSASS database cache depends on the “transition pages repurposed/second” perfmon counter, a pagefile is required to make sure that the database cache is capable to release memory if memory is requested by other services or applications.

 

INTRODUCTION

When you set up a 64-bit version of Microsoft Microsoft Windows Server 2008 and Microsoft Windows Server 2008 R2, the operating system will create a page file that is  auto managed (Automatically manage paging file size for all drives) in your computer. However, as the amount of RAM in a computer increases, the need for a page file may decrease. The following guidelines and methods will help you determine the appropriate page file size for your system.

Comparison of memory and CPU limits in the 32-bit and 64-bit versions of Windows

When you set up a 64-bit version of Windows Server 2008 or  Windows Server 2008 R2, a page file is created that is depeding on how much RAM is installed and provided there is sufficient free space on the system hard disk:

The more RAM that you have available or is added to a computer,  it generally tends to decrease the size of the page file needed.  If you have enough RAM installed in your computer, you may not require a page file at all, unless one is required by a specific application.  This all depends on how much virtual memory is used by your system and/or applications installed.

 

System Memory Size (RAM)	Minimum Page File Size	Maximum Page File Size
Windows XP and Windows Server 2003 <1GB	1.5 x RAM	3 x RAM
Windows XP and Windows Server 2003 >= 1GB	1 x RAM	3 x RAM

Table 1.  Default Page File Sizes for Windows XP and Windows Server 2003.

System Memory Size (RAM)	Minimum Page File Size	Maximum Page File Size
<1GB	Large enough to hold a kernel-memory crash dump and is RAM plus 300MB or 1GB, whichever is larger	3 x RAM or 4GB, whichever is larger
>= 1GB	Large enough to hold a kernel-memory crash dump and is RAM plus 300MB or 1GB, whichever is larger	3 x RAM or 4GB, whichever is larger

 

Click here to read the full Microsoft Support Article