Decreasing number of CPUs on multiple VMs

[Arkady]

Hello,

We have many VMs with over provisioned CPUs, need to remove 1 CPU from them.

Appreciate any help.

Thank you in advance!

[LucD]

Is there a list of VMs, in a text file?
Are these VMs powered off?

Or does the script need to take care of that?

And do all the VMs have the VMware Tools installed and running?

[LucD]

This is for a specific VM.
The script checks the powerstate, and brings the VM back to that state when the CPU number is lowered by 1.

Also I builtin a safety for VMs that only have 1 vcpu

$vmName = 'MyVM'

foreach($vm in Get-VM -Name $vmName){

    if($vm.NumCpu -ne 1){

        $wasPoweredOn = $false

        if($vm.PowerState -ne 'PoweredOff'){

            $wasPoweredOn = $true

            Shutdown-VMGuest -VM $vm

            while($vm.PowerState -ne 'PoweredOff'){

                sleep 5

                $vm = Get-VM -Name $vm.Name

            }

        }

        $vm = Set-VM -VM $vm -NumCpu ($vm.NumCpu - 1) -Confirm:$false

        if($wasPoweredOn){

            Start-VM -VM $vm -Confirm:$false

        }

    }

    else{

        Write-Output "VM $vm.Name only has 1 vcpu"

    }

}

[Arkady]

Yes, there will be a list of VMs in a text file.

These VMs are powered on with VMware tools installed

[LucD]

That is a slight modification of the previous script

$vmnames = '.\vmnames.txt'

foreach($vm in Get-VM -Name (Get-Content -Path $vmnames)){

    if($vm.NumCpu -ne 1){

        $wasPoweredOn = $false

        if($vm.PowerState -ne 'PoweredOff'){

            $wasPoweredOn = $true

            Shutdown-VMGuest -VM $vm

            while($vm.PowerState -ne 'PoweredOff'){

                sleep 5

                $vm = Get-VM -Name $vm.Name

            }

        }

        $vm = Set-VM -VM $vm -NumCpu ($vm.NumCpu - 1) -Confirm:$false

        if($wasPoweredOn){

            Start-VM -VM $vm -Confirm:$false

        }

    }

    else{

        Write-Output "VM $vm.Name only has 1 vcpu"

    }

}

[Arkady]

Thank you!

I will test and let you know.

[Arkady]

These VMs are Windows 7 and support maximum 2 CPUs but any number of cores.

So to configure 3 CPUs VM has 1 CPU and 3 cores  for example. So to decrease a number of CPUs we need to decrease a number of cores.

Would be possible to modify the script?

[LucD]

If you 1 CPU block with 3 cores and you change NumCPU to 2, you will end up with 1 CPU block with 2 cores.

Or do you mean something else?

[Arkady]

Current configuration for example 1 CPU and 3 cores. Need to change to 1 CPU and 2 cores instead

[LucD]

Ok, got you.

Try like this, but note that this solution has a flaw if you have more than 1 CPU block.

Assume you have configured 2 CPU blocks, each with 3 cores. That gives 6 for NumCPU.

Lowering that to 5 will not work, you can only lower to 4, and change the CoresPerBlock from 3 to 2.

$vmName = 'MyVM'

foreach($vm in Get-VM -Name $vmName){

   if($vm.NumCpu -ne 1){

   $wasPoweredOn = $false

   if($vm.PowerState -ne 'PoweredOff'){

   $wasPoweredOn = $true

  Shutdown-VMGuest -VM $vm

   while($vm.PowerState -ne 'PoweredOff'){

  sleep 5

   $vm = Get-VM -Name $vm.Name

   }

   }

   if($vm.CoresPerSocket -gt 1){

     $vm = Set-VM -VM $vm -NumCpu ($vm.NumCpu - 1) -CoresPerSocket ($vm.CoresPersocket - 1) -Confirm:$false

   }

   else{

     $vm = Set-VM -VM $vm -NumCpu ($vm.NumCpu - 1) -Confirm:$false

   }

   if($wasPoweredOn){

   Start-VM -VM $vm -Confirm:$false

   }

   }

   else{

   Write-Output "VM $vm.Name only has 1 vcpu"

   }

}

[Arkady]

This is what happened - please attached screen shot

Changed Total number of cores to 2 but still report Number of cores per socket as 3

[LucD]

Did you start the VM?

[Arkady]

Yes

[LucD]

That seems ot be an issue with the Set-VM cmdlet, because it actually says total number of cores is 2.

While the cores per socket keeps saying 3.

Perhaps we should try the ReconfigVM method?

[Arkady]

Not familiar with this

[LucD]

Try this way.

$vmName = 'MyVM'

foreach($vm in Get-VM -Name $vmName){

   if($vm.NumCpu -ne 1){

   $wasPoweredOn = $false

   if($vm.PowerState -ne 'PoweredOff'){

   $wasPoweredOn = $true

  Shutdown-VMGuest -VM $vm

   while($vm.PowerState -ne 'PoweredOff'){

  sleep 5

   $vm = Get-VM -Name $vm.Name

   }

   }

   if($vm.CoresPerSocket -gt 1){

   $spec = New-Object VMware.Vim.VirtualMachineConfigSpec

   $spec.NumCoresPerSocket = $vm.CoresPersocket - 1

   $spec.NumCPUs = $vm.NumCpu - 1

   $vm.ExtensionData.ReconfigVM($spec)

   }

   else{

   $vm = Set-VM -VM $vm -NumCpu ($vm.NumCpu - 1) -Confirm:$false

   }

   if($wasPoweredOn){

   Start-VM -VM $vm -Confirm:$false

   }

   }

   else{

   Write-Output "VM $vm.Name only has 1 vcpu"

   }

}

[Arkady]

Unfortunately same result

[LucD]

Works for me.
No clue why it doesn't work for you.

Which vSphere version are you using?

[LucD]

It looks as if the CoresPerSocket behaviour has been changed in vSphere 6.5.

I tested my script in vSphere 6.7.
If you're on vSphere 6, or older, that might explain our different results.

Frank's post Decoupling of Cores per Socket from Virtual NUMA Topology in vSphere 6.5​

gives some more details on this.