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ACPI motherboard layout requires EFI - Considerations for switching VM firmware in vSphere 8 

01.11.2023 by William Lam // 1 Comment

One of the important settings to consider when creating a new Virtual Machine in vSphere is the VM firmware, which can either be BIOS or EFI and can be configured under VM Options->Boot Options->Firmware. After selecting the desired guest operating system (GOS) in vSphere, the system will default to a recommended firmware type and can also be overridden by the user. Ultimately, the selection of the VM firmware should be determined by what your GOS supports.

If you ever need to change the VM firmware, you typically will need to re-install the GOS because it does not understand the new firmware change (just like in a physical server) and more than likely the GOS will also not boot due to this change and this is the existing behavior from GOS point of view.

For a net new VM creation, prior to vSphere 8, if you had configured a VM using EFI firmware and you have not installed a GOS and realized that you had made a mistake and needed to change the VM firmware to BIOS, you could easily do so using the vSphere UI or API and then install your OS. In vSphere 8 and specifically when using the latest Virtual Machine Compatibility (vHW20), you can not just switch the VM firmware after the initial VM creation, especially if you had started with EFI firmware and wish to change it to BIOS.

In doing so, you will come across the following error message:

ACPI motherboard layout requires EFI. Failed to start the virtual machine. Module DevicePowerOnEarly power on failed.

[Read more...]

Categories // vSphere 8.0 Tags // acpi, bios, ESXi 8.0, i440bx, UEFI, vNUMA, vSphere 8.0

Virtual NUMA (vNUMA) and CPU Hot-Add support in vSphere 8

11.21.2022 by William Lam // 1 Comment

While looking for something in the vSphere 8.0 API Reference, I stumbled onto a new VM configuration setting in vSphere 8 called exposeVnumaOnCpuHotadd which looks quite interesting and has the following description:

Capability to expose virtual NUMA when CPU hotadd is enabled. If set to true, ESXi will consider exposing virtual NUMA to the VM when CPU hotadd is enabled. If set to false, ESXi will enforce the VM to have single virtual NUMA node when CPU hotadd is enabled. If unset, the VM continue to follow the behavior in last poweron.

This actually reminded me of question that we got during one of our vSphere 8 Meet the Experts (MTE) sessions at VMware Explore Barcelona and whether there were any new enhancements to vNUMA when CPU hot-add is enabled, which I was not aware of any at the time. The vNUMA and CPU Hot-Add issue is detailed in this blog post by no other than my buddy Frank Denneman and here is a quick summary of the issue:

CPU Hot-Add is not compatible with vNUMA, if hot-add is enabled the virtual NUMA topology is not exposed to the guest OS and this may impact application performance.

[Read more...]

Categories // Automation, vSphere 8.0 Tags // vNUMA, vSphere 8.0

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William is Distinguished Platform Engineering Architect in the VMware Cloud Foundation (VCF) Division at Broadcom. His primary focus is helping customers and partners build, run and operate a modern Private Cloud using the VMware Cloud Foundation (VCF) platform.

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