Deans Blog

In a non-production environment I was required to create a large number of small workload virtual machines on a ESXi hosts. Following provisioning of the virtual machines and during the power on stage I received the following error message to which I was no longer able to power on additional virtual machines on a particular host system.

An error was received from the ESX host while powering on VM vm186.
Failed to start the virtual machine.
Failed to power on VM.Could not power on VM : msg.vmk.status.VMK_VCPU_LIMIT_EXCEEDED.
Max VMs limit reached: 184 (32768 worlds)

On investigation, by default  the maximum number of vCPUs that should run on a single core on a ESXi Hosts is determined at runtime. It is possible (whilst not recommended or supported) to configure this behaviour by modifying the kernel settings for the host system using the vSphere Command-Line Interface.

To provide a workaround to the above error message is to modify the value of the ‘maxVCPUsPerCore’ in the kernel settings, firstly we will list the default values.

~ # esxcli system settings kernel list -o maxVCPUsPerCore
Name             Type     Configured  Runtime  Default
maxVCPUsPerCore  uint32    0           0        0

Now we will modify the value, in this example to configure the maximum number of vCPUS per core to be ‘1000’.

~ # esxcli system settings kernel set -s maxVCPUsPerCore -v 1000

In my example, the virtual machines will be configured with a single vCPU, and therefore I will also modify the maximum number of virtual machines on the host to also be ‘1000’.

~ # esxcli system settings kernel set -s maxVMs -v 1000

In order to apply the configuration change the host system will require a restart.