Andre Leibovici, a fellow vExpert who works for EMC as a Sr. vSpecialist has blogged today about an issue with HP Blades and a power regulation setting where the default on HP Blades can cause performance issues. http://myvirtualcloud.net/?p=1212

This is one of those great finds as it can be so difficult to troubleshoot “My VM is running slow” and you can go through your virtualisation environment with a fine tooth comb and find nothing as the issue is actually related to hardware settings.

Interestingly the issue manifests itself when the system is not fully utilised and CPU use is not high as Power Regulation only kicks in when it sees there are idle CPU cycles which makes it even more confusing to troubleshoot as you would be getting high CPU READY figures when CPU wasn’t stretched.

HP has a document, Power Regulator for ProLiant servers which explains it all. http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00300430/c00300430.pdf

The fix is to either disable Power Regulator on the hardware BIOS by setting it to Static High Performance mode which will disable any power savings or set it to a custom setting, OS Control mode and then configure ESX(i)‘s Power Management Policy using the vSphere Client Host Configuration panel to High Performance to disable power management.

Thanks, Andre!