8-way VM on ESX 4.1 - Win2k8 R2 Standard edition

Today, I had to configure a VM with 8 vCPU's on an ESX 4.1 cluster. The guest OS was Windows Server 2008 R2 Standard Edition. However, after configuring the VM with 8 vCPU's it still only registered 4 vCPU's in the guest OS.

The reason is that both Win2k3 and Win2k8 R2 standard edition only can be configured with four physical CPUs or sockets. By default vSphere 4.0 and 4.1 presents 1 vCPU as one socket.

To bypass this, there is a feature (experimental in 4.0 but supported in 4.1) allowing you to configure multiple cores per socket. See this KB article. This feature has been included in vSphere 5.0 in the GUI.

See this article for comparison of Windows 2003 editions.

See this link for comparison of Windows 2008 edition (look for 'Editions Guide' at the bottom of the page). Or download PDF here.

CPU compability tool

This tool from run-virtual.com can be used to check the CPU compability of your physical servers. On many servers, the VT feature is disabled by default which means that 64-bit VM's cannot run. With this tool, this can be checked without having to boot into BIOS.