How big should Windows NT paging file be?

How big should you set Windows NT pagefile? Microsoft’s forumla
definition is size of RAM + 12MB or 2.5 X size of SAM file, whichever is larger.
If you have 128MBs of RAM, that works out to 140MB. The traditional unix advice
for pagefile is 2xRAM which would work out to 256MB. The maximum legal page size
for Windows NT and Windows 2000 is 4095MB.

The only downside to a too large page file size is that you are consuming
some of your disk space unneccessarily. Given the size of modern disks, this
seems to be a trivial issue. Under Windows NT, the page file occupies a
contiguous block of space in the partition. If possible split the page file
between hard disks. Don’t split the page file across partitions created on the
same hard drive since that will decrease performance.

Anyone who has used a defrag tool like Diskeeper with a graphic disk map,
sees the huge contiguous chunk of the page file in NT. Windows 2000 does not
have the contiguous block requirement.

The downsides of a too small pagesize are much more serious. At a minimum,
your system will experience disk thrashing where your pagefile files to maximum
and NT is constantly swapping out segments of RAM to disk virtual memory. This
can really impact performance. It can also result in a corrupted pagefile.
Additionally, the pagesize should be at least the size of RAM+1MB in order to
support core dumps. In any case, you have swapped out the fasted component in
your server for the slowest. Given these factors, I recommend the unix formula.

One of Windows 2000 improvements is more control of core dumps. Windows 2000
has three sets:

  • none
  • Small memory dump (64K)
  • Kernel memory dump
  • Complete memory dump
Windows NT has the Complete
memory dump
or none. If you have a lot of RAM, I would pick the Kernel memory dump option. To set these options in Windows

  • Double-click on the System Applet in Control Panel
  • Select the Advanced Tab
  • Click on Startup and Recovery

For more information on dump files (.dmp files) see:

Blue Screen Information After Memory Dump
2000 Memory Dump Options Overview

Dumpchk.exe to Check a Memory Dump File
Small Memory Dump Files Created by Windows 2000

But, note that but (:->, although I have never seen the unix
formula to be too small, the actual pagesize might need to be bigger under some
unique set of factors. The only way to be absolutely sure, one must use diskperf
and monitor the pagefile usage peak object. For
information to help with this task, read kb article :

to Monitor Disk Performance with Performance Monitor

Page Files for Optimization and Recovery

System Internals has released a freeware tool, PageDefrag , which will
generate a fragmentation report and will defragment Windows NT 4’s pagefile and
registry. Windows NT is very bad about fragmentation.

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