ArcGIS processes are taking much longer to run on Windows Server 2012 than Windows Server 2008

Description

After moving from a system running Windows Server 2008 to one running Windows Server 2012, a noticeable increase in the amount of time it takes to complete geoprocessing tasks can occur.

Cause

This is a known issue with Windows Server 2012 when doing a Remote Desktop Session Host via RDP. This issue does not occur with Windows 2008 servers.

The reason for this is because of Fair Share CPU Scheduling being added to the Remote Desktop Services in Windows Server 2012. This did not exist in Windows Server 2008. Fair Share CPU Scheduling distributes the CPU time across all active sessions based on the number of sessions, not the load or priority. By turning off CPU sharing, this should resolve the issue.

Solution or Workaround

Warning:
WARNING: The instructions below include making changes to essential parts of your operating system. It is recommended that you backup your operating system and files, including the registry, before proceeding. Consult with a qualified computer systems professional, if necessary. 

Esri cannot guarantee results from incorrect modifications while following these instructions; therefore, use caution and proceed at your own risk. 

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\SessionManager\DFSS\EnableDFSS