Having trouble hot adding vCPUs to Windows Server 2012?

Administrators don’t like to bring down running workloads if it can be helped, particularly in 24/7 environments.  As such, the ability to hot add resources – that is, add additional resources to a running virtual machine – such as RAM and CPUs is important to many.

For those that are running the latest and greatest – vSphere 5.1 and Windows Server 2012 – this feature may be a bit problematic due to a known issue, but the issue only manifests itself in specific circumstances:

  • You must be running vSphere 5.1 on the host
  • The virtual machine must be running Windows Server 2012 Data Center
  • The virtual machine is configured to use hardware version 9

In these instances, administrators are able to actually add the resources to the virtual machine, but those resources don’t actually become available.  Until a fix is implemented, VMware recommends using virtual machine hardware version 8, which is not affected by the issue.

For more information, visit the support page on this issue.

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