Change bios to UEFi after installing ESXi – would like to hear your opinion

Hi everyone,

I have a R710 Dell server running VMware ESXi 6.7 for a year+ now without trouble. I’ve bought a NVME drive + PCIe adapter (because it was cheaper than SSD for it’s size) to run my VMs on (need to migrate the current VMs to the new drive).

The thing is that I need to enable UEFI for the NVME drive to work. Right now the physical server which runs ESXi is booting from bios.

**What VMware says about this:**

ESXi Booting Requirements vSphere 6.7 supports booting ESXi hosts from the Unified Extensible Firmware Interface (UEFI). With UEFI, you can boot systems from hard drives, CD-ROM drives, or USB media. Starting with vSphere 6.7, VMware Auto Deploy supports network booting and provisioning of ESXi hosts with UEFI. ESXi can boot from a disk larger than 2 TB if the system firmware and the firmware on any add-in card that you are using support it. See the vendor documentation.

*Note Changing the boot type from legacy BIOS to UEFI after you install ESXi 6.7 might cause the host to fail to boot. In this case, the host displays an error message similar to Not a VMware boot bank. Changing the host boot type between legacy BIOS and UEFI is not supported after you install ESXi 6.7.*


So, my question is if anyone has experience doing this? Or could someone guess if this will actualy break stuff or just switching back to bios will fix the problem, and no harm done?

Hope someone has experience doing this, or could test it?

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  1. You will need to reinstall when switching to/from BIOS and UEFI. It would be best to move your VMs to other storage and format the original install location to remove the ESXi vFAT partitions. If you can’t pay attention to the installer and you can preserve your VMFS datastores.

  2. Backup your VMs with Veeam CE to some external storage, replace the drives, switch to UEFI, and reinstall from scratch. Restore the VMs as soon as everything is up and running.

    That would be the cleanest approach and will surely work. I doubt you will be able to boot up ESXi after switching from legacy boot to UEFI. And I can not reassure you will be able to boot again after switching things back either.

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