Hyper-V VM Slow on Windows Server 2008 R2

I recently upgraded my virtual machine hosting server from Window Server 2008 to Windows Server 2008 R2. There are some noticeable performance drop, especially on virtual machines that handles big log files, the automation script execution time can take 200% or more than it was in a VMHOST with Windows Server 2008.

I have done some testing and the performance downgrade seem introduced by the new power management system in windows server 2008 R2. There are 3 build in power plan in Windows Server 2008 R2

• Balanced (recommended)
• High Performance
• Power Saver

The default power plan in Windows Server 2008 R2 is Balanced. After I change Power Plan to High Performance and the performance downgrade issue does no occur any more. My guess is when power plan is set to balance, applications might not full utilize all available hardware resources.

You can also checkout this post for Set the power configuration to High Performance in scripts.