Monday, June 27, 2016

ESXi boot mode - UEFI or BIOS

Legacy BIOS bootstrapping along with a master boot record (MBR) is uses with x86 compatible systems for ages. The concept of MBRs was publicly introduced in 1983 with PC DOS 2.0. It is unbelievable that we are still using the same concept after more then 30 years.

However, there must be some limitations in 30 years old technology, isn't it?

BIOS limitations (such as 16-bit processor mode, 1 MB addressable space and PC AT hardware) had become too restrictive for the larger server platforms. The effort to address these concerns began in 1998 and was initially called Intel Boot Initiative later renamed to EFI. In July 2005, Intel ceased its development of the EFI specification at version 1.10, and contributed it to the Unified EFI Forum, which has evolved the specification as the Unified Extensible Firmware Interface (UEFI).

What is EFI (or UEFI) firmware?

UEFI replaces the the old Basic Input/Output System (BIOS). UEFI can be used on

  • physical server booting ESXi hypervisor or 
  • Virtual Machine running on top of ESXi hypervisor. 
This blog post is about ESXi boot mode however just for completeness I would like to mention that VMware Virtual Machine with at least hardware version 7 supports UEFI as well. For further information about VM UEFI look at [1].

Originally called Extensible Firmware Interface (EFI), the more recent specification is known as Unified Extensible Firmware Interface (UEFI), and the two names are used interchangeably.

EFI (Extensible Firmware Interface) is a specification for a new generation of system firmware. An implementation of EFI, stored in ROM or Flash RAM, provides the first instructions used by the CPU to initialize hardware and pass control to an operating system or bootloader. It is intended as an extensible successor to the PC BIOS, which has been extended and enhanced in a relatively unstructured way since its introduction. The EFI specification is portable, and implementations may be capable of running on platforms other than PCs.
For more information, see  the Wikipedia page for Unified Extensible Firmware Interface.

General UEFI Advantages

UEFI firmware provides several technical advantages over a traditional BIOS system:

  • Ability to boot from large disks (over 2 TB) with a GUID Partition Table (GPT)
  • CPU-independent architecture
  • CPU-independent drivers
  • Flexible pre-OS environment, including network capability
  • Modular design
  • Since UEFI is platform independent, it may be able to enhance the boot time and speed of the computer. This is especially the case when large hard drives are in use. 
  • UEFI can perform better while initializing the hardware devices.
  • UEFI can work alongside BIOS. It can sit on top of BIOS and work independently.
  • It supports MBR and GPT partition types.

Note: Modern systems are only emulating the legacy BIOS. They are EFI native.


vSphere 5.0 and above supports booting ESXi hosts from the Unified Extensible Firmware Interface (UEFI). With UEFI, you can boot systems from hard drives, CD-ROM drives, USB media, or network.

UEFI benefits

  • ESXi can boot from a disk larger than 2 TB provided that the system firmware and the firmware on any add-in card that you are using supports it. 

UEFI drawbacks

  • Provisioning with VMware Auto Deploy requires the legacy BIOS firmware and is not available with UEFI BIOS configurations. I hope that this limitation will be lifted soon.

Notes: Changing the host boot type between legacy BIOS and UEFI is not supported after you install ESXi 6.0. Changing the boot type from legacy BIOS to UEFI after you install ESXi 6.0 might cause the host to fail to boot.


UEFI is meant to completely replace BIOS in the future and bring in many new features and enhancements that can’t be implemented through BIOS. BIOS can be used in servers that do not require large storage for boot. To be honest, even you can, it is not very common to use boot disks greater then 2 TB for ESXi hosts therefore you may be using BIOS at the moment, but I would recommend shifting to UEFI, as it is the future while BIOS will fade away slowly.

ESXi hypervisor supports both boot modes therefore if you have modern server hardware and don't use VMware Auto Deploy then UEFI should be your preferred choice.

[1] VMware : Using EFI/UEFI firmware in a VMware Virtual Machine 
[2] VMware : Best practices for installing ESXi 5.0 (VMware KB 2005099)
[3] VMware : Best practices to install or upgrade to VMware ESXi 6.0 (VMware KB 2109712)
[4] Usman Khurshid : [MTE Explains] Differences Between UEFI and BIOS
[5] Wikipedia : Unified Extensible Firmware Interface

Thursday, June 16, 2016

Role and responsibility of IT Infrastructure Technical Architect

In this article, I would like to describe the infrastructure architect role and his responsibility.

Any architect generally leads the design process with the goal to build the product.  The product can be anything the investor would like to build and use. The architect is responsible to gather all investor's goals, requirements, constraints and try to understand all use cases of the final product.

The product of IT technical infrastructure architect is an IT infrastructure system, also known as a computer system, running an IT applications supporting business services. That's very important statement. Designed IT infrastructure system is usually not built just in sake of infrastructure itself but to support business services.

There is no doubt that the technical architect must be a subject matter expert in several technical areas including computing, storage, networking, operating systems and applications but that's just a technical foundation required to fulfill all technical requirements. However, systems are not impacted just by technology but also by other external non-technical factors like business requirements, operational requirements and human factors. It is obvious that the architect's main responsibility is to fulfill all these requirements of the final product, IT infrastructure system in this particular case, although the last mentioned factor, a human factor, usually has the biggest impact on any systems design because we usually build systems for human usage and these systems has to be also maintained and operated by other humans as well.

Now, when we know what the IT Infrastructure Technical Architect does, let's describe what are his typical tasks and activities.

The Architect has to communicate with investor's stakeholders to gather all design factors including requirements, constraints and use cases. Unfortunately, there are usually also some design factors nobody have a specific requirement. These factors has to be documented as assumptions. When all relevant design factors are collected and revalidated with requestors and investor authorities, the architect starts design analysis and prepare conceptual design. The conceptual design is a high level design which helps to understand the overall concept of proposed product. Such conceptual design has to be reviewed by all design stakeholders and when everybody feels comfortable with the concept the architect can start low level design.

Low level design is usually prepared as decomposition of conceptual design. Low level design should be decomposed into several design areas because it is almost always beneficial to divide complex system into sub-systems until these become simple enough to be solved directly. This decomposition approach is also known as "Divide and conquer" method. The main purpose of low level design is to document all details important for successful implementation and operation of the product. Therefore it must be reviewed and validated by particular subject matter experts - other architects, operators, and implementers - for particular area. The low level design is usually divided into logical and physical design. Logical design is detailed technical design but general logical components are used without using a particular suppliers physical product models. materials, configuration details or other physical specifications. The purpose of logical design is to document general principles principles of overall design or particular decomposed, thus simplified, design area. Logical design is also used for proper product sizing and capacity planning. Physical design, on the other hand, is detailed technical design with specific products, materials and implementation details. Physical design is primarily intended to product builders and implementors because the product is build or implemented based on the physical design.

It is good to mention that there is no product or system without a risk. That's another responsibility of the architect. He should identify and document all risks and design limitations associated with proposed product. The biggest threats are not risks in general but unknown risks. Therefore, potential risks documentation and risk mitigation options is very important architect's responsibility. Risk mitigation plan or at least contingency plan should be the part of product design.

At the end of the day, the design should be implemented therefore the implementation plan is just another activity and document the architect must prepare to make the product real even the implementation is usually out of the architect scope.

It is worth to mention, that here is no proven design without design tests. Therefore the Architect should also prepare and perform the test plan. Test plan have to include validation and verification part. Validation part validates design requirements after product build or implementation. Only after validation, the architect can honestly proof that the product really fulfill all requirements holistically. Verification part verifies that everything was implemented as designed and operational personnel knows how to operate and maintain the system.

There is no perfect design nor product, therefore the architect should continually improve even already built product by communication with end users, operators and other investor stakeholders and take their feedback in to account for future improvements. After some period of time, the architect should initiate design review and incorporate all gathered feedback in to the next design version.

Now, when we know what the architect is responsible for let's summarize what skills are important for any good architect. The architect must have following decent skills and expertise:

  • communication skills
  • presentation skills
  • consulting skills
  • cross check validation skills
  • documentation skills
  • systematic, analytical, logical and critical thinking
  • technical expertise
  • ability to think and work in different levels of detail
  • ability to see a big picture but also have attention for detail because the devil is in the details
Even you have read this article to this point, you can ask what is the architect main responsibility. That's a faire question. Here is short answer.

The architect main responsibility is the happiness of all users and actors using designed product during the whole lifecycle of the product.

Wednesday, June 01, 2016

Force10 Operating System 9.10 changes maximum MTU size

Force10 operating system (aka FTOS, DNOS) always had the maximal configurable MTU size per port 12000 bytes. I have just been informed by former colleague of mine that it is not the case since FTOS 9.10 and above. Since FTOS 9.10 the maximum MTU size per switch port is 9216. If you used MTU 12000 then after upgrade to firmware 9.10 the MTU should be adjusted automatically. But I have been told that it is automatically adjusted to standard MTU 1500 therefore if you use Jumbo Frames (9000 bytes payload) it is necessary to change configuration before upgrade from 12000 to 9216.

Disclaimer: I had no chance to test it so I don't guarantee all information on this post are correct. 

UPDATE: Please read comments below this article for further information and great Martin's explanation of real MTU behavior. Thanks Martin and Kaloyan for your comments.

Martin's comment:
MTU 12000 in configuration was not reflecting real hardware MTU of underlaying chipset, after upgrade to 9.10 it's just adjusted to reflect real hardware MTU. Tested on S4048 9.10(0.1). When you boot into 9.10 you can see log messages saying that configuration is adjusted to reflect real maximum hardware MTU.
Also in configuration

 ethswitch1(conf-if-te-1/47)#mtu ?  
 <594-12000> Interface MTU (default = 1554, hardware supported maximum = 9216)