What is UEFI?

UEFI stands for Unified Extensible Firmware Interface. The UEFI specification defines a new model for the interface between operating systems and platform firmware. UEFI is designed to replace BIOS(Basic Input / Output System) firmware interface.

Advantages of choosing a UEFI boot mode installation includes the following:

  • Supports disks and partitions greater than 2TB, includes support for even booting the operating system.               
  • It includes "boot manager", which is in charge of loading the OS loaders and all necessary drivers. As a result, bootable operating system images will appear in the boot list as labeled entities, for example Red Hat Enterprise Linux.
  • It supports MBR and GPT partition types.

VMware ESXi support for UEFI:

VMware supports installing / booting ESXi hosts in UEFI boot mode from ESXi 5.0 onwards. There is no support available in VMware ESX/ESXi 4.0.x/4.1.x branch for UEFI. Refer to VMware KB which talks about best practices while using ESXi in UEFI mode.

Dell Support for UEFI on PowerEdge servers:

Dell supports UEFI from 11th  generation of PowerEdge servers onwards. For a list of PowerEdge servers based on different generations, refer to wiki.

To toggle the boot mode from BIOS to UEFI and vice versa on Dell PowerEdge servers, Press F2 key (System Setup) --> Select System BIOS --> Go to Boot Settings --> Select BIOS if you want to boot the system in BIOS boot mode and select UEFI if you want to boot the system in UEFI boot mode.

To buy a Dell PowerEdge Server  factory installed  with VMware ESXi system with UEFI boot mode:

  • If you order a system via Dell online, the UEFI boot mode option is not available. Hence factory installation slices the virtual disks into 1.8 TBs in BIOS boot mode.
  • Contact the Dell Sales Team to order a factory installed ESXi system with UEFI boot mode and virtual disk size of >= 2 TB.

Limitations:

  • Network boot of VMware ESXi or provisioning with VMware Auto Deploy requires the legacy BIOS firmware and is not available with UEFI. 
  • Booting ESXi from an iSCSI target is not supported in UEFI boot mode. Refer to “ESXi Booting Requirements” section available in VMware document .

References:

www.uefi.org

http://en.community.dell.com/techcenter/b/techcenter/archive/2012/06/22/esxi-boot-failure-with-uefi-boot-mode.aspx