By default, you cannot add CPU resources to a virtual machine when the virtual machine is turned on. The CPU hot add option lets you add CPU resources to a running virtual machine.

The following conditions apply.

  • For best results, use virtual machines that are compatible with ESXi 5.0 or later.
  • Hot adding multicore virtual CPUs is supported only with virtual machines that are compatible with ESXi 5.0 or later.
  • If a virtual machine has 128 virtual CPUs or less, you cannot use hot adding to further increase the number of virtual CPUs. To change the number of virtual CPUs beyond that limit, you must first power off the virtual machine. By contrast, if a virtual machine already has more than 128 virtual CPUs, you can use hot adding to further increase the number of virtual CPUs to up to 256.
  • Not all guest operating systems support CPU hot add. You can disable these settings if the guest is not supported.
  • To use the CPU hot add feature with virtual machines that are compatible with ESXi 4.x and later, set the Number of cores per socket to 1.
  • Adding CPU resources to a running virtual machine with CPU hot add enabled disconnects and reconnects all USB passthrough devices that are connected to that virtual machine.

Prerequisites

  • Verify that the virtual machine is configured as follows.
    • Latest version of VMware Tools installed.
    • Guest operating system that supports CPU hot add.
    • Virtual machine compatibility is ESX/ESXi 4.x or later.
    • Virtual machine is turned off.
  • Required privileges: Virtual Machine.Configuration.Settings

Procedure

  1. Right-click a virtual machine in the inventory and select Edit Settings.
  2. On the Virtual Hardware tab, expand CPU, and select Enable CPU Hot Add.
  3. Click OK.

Results

You can now add CPUs even if the virtual machine is turned on.
Note: Hot adding virtual CPUs to a virtual machine with NVIDIA vGPU requires that the ESXi host have a free vGPU slot.