ESXi 6.7 install on UEFI or BIOS

[virtualizingtheworld]

Hi,

Is there any best practice recommendation that specifies if the latest ESXi should be install in UEFI or BIOS?

Got new servers which default to UEFI so not sure if perfectly fine to proceed without changes?

It seems that once the ESXi is installed on a specific mode, you cannot change it after as the ESXi won't boot.

Thanks

[a_p_]

Although both modes should work, I'd go with the UEFI mode, which btw. is the default option for many current operating systems.

André

[virtualizingtheworld]

Ok, do you know if that can be changed afterwords (not sure why) to BIOS or this would require ESXi to be re-installed?

[a_p_]

I can't tell you for sure whether this will work, because I never tried it. I've been setting up ESXi host in UEFI mode for years now, and never experienced any issues due to this.

André

[Alex_Romeo]

HI,

I agree with a.p. better EUFI.

I'll add the "VMware ESXi Installation and Setup" manual which has important points for your post (from page 11).

ARomeo

[virtualizingtheworld]

That's helpful with further information....this part answers the question:

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.

This means that if I need to update the Server firmware and the bootable media does not boot in UEFI mode, I will temporarily change the boot mode to BIOS to perform the update and then change back to UEFI

[mduregon]

the original post stated

It seems that once the ESXi is installed on a specific mode, you cannot change it after as the ESXi won't boot

a later post added

... might cause the host to fail to boot ...

but from a different discussion  https://communities.vmware.com/message/2633881#2633881​

Unlike Linux or Windows, ESXi has no such distinction as UEFI install versus legacy BIOS install. You can freely switch your host back and forth between UEFI and legacy BIOS after installation and ESXi will continue to boot

Hope this helps

Marino

[Darius Davis]

When ESXi is installed to a storage device (hard disk or whatever), I'm fairly sure that the contents of that storage device will not depend on the firmware type used during installation.  The same storage device can subsequently be used for either BIOS boot or EFI/UEFI boot.

The risk when changing a host between BIOS and EFI/UEFI is that the system firmware might need to be "taught" how to boot the OS.  EFI/UEFI implementations will often not boot an operating system unless they've been configured with a Boot Option which describes the installed OS, where to find its bootloader, and how to launch that bootloader.  If ESXi is installed in BIOS mode and is then switched to EFI/UEFI, you might need to perform a few extra steps in your firmware setup utility before ESXi can boot.  In theory the same applies for conversions going the other way: Some EFI/UEFI implementations might need to be explicitly configured to boot a legacy OS from the storage device, but it is much more common for that combination to boot successfully without any extra effort.

So... it sounds like splitting hairs, but the summary (to the best of my current understanding) is:

• ESXi installs "the same way" in both BIOS and EFI/UEFI, with the same on-disk layout and contents, but
• booting ESXi on a particular system might require host firmware configuration steps which are specific to the host firmware and boot method (BIOS/[U]EFI), so it might require manual configuration before it can boot through the "other" firmware, hence the element of risk in doing that.

Thanks,

--

Darius

[coldfix]

I highly discommend trying such an approach as switching between UEFI and BIOS.

The problem is, if your BIOS does not support GPT, while UEFI does, you won't be able to start the OS.

The problem with installing in BIOS mode and then switching to UEFI is less than 8 required partitions for normal functioning UEFI mode, because:

1)BIOS installation created <4 partitions

2)repartitioning is a work

3)MBR supports only 4 primary partitions to boot from

 

So answer is: use the latest technology - (U)EFI.