Which kind of guest OS are you using?

Andre

Where is the poster go? Anyways, have you check if ESX host is vSMP aware and licensed for that feature? If yes, when you change from 1vCPU to vSMP, it will automatically changes the CPU HAL to multiprocessor, if not, you may want to access "Device Manager" and go through the wizard to see if it show up! But get back here and answer types of OS for the VM!

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Regards,

Stefan Nguyen
VMware vExpert 2009
iGeek Systems Inc.
VMware, Citrix, Microsoft Consultant

Glad its working and nice to know the workaround? I'm still curious why it doesn't work when edit the virtual machines! Is the machine create from scratch using vCenter or P2V'ed from physical to virtual?

If you found this information useful, please consider awarding points for "Correct" or "Helpful". Thanks!!!

Regards,

Stefan Nguyen
VMware vExpert 2009
iGeek Systems Inc.
VMware, Citrix, Microsoft Consultant

Are you trying the hot add CPU while the VM is running? And some OS need to have the driver before the hardware is installed (Yes I know in a VM you don't actually install anything, but the OS doesn't know it's in a VM). So you might upgrading the kernel / Windows OS HAL then power off, then add the CPU. That sometimes works better.