With the release of vSphere 4.1 it will be the last version of ESX to be released in an ESX and an ESXi version. After this version only the ESXi flavor will be released. We at VMGuru.nl predicted that this would happen a few years back, so we advised our customers to go for the ESXi version, too make it a lot easier to migrate to a newer version in the future.

VMware recommends that customers deploy vSphere 4.1 on the ESXi hypervisor architecture as a best practice.

In the past some features from the ESX architecture weren’t supported on the ESXi platform. As of vSphere 4.0, all the functionality of VMware vSphere is supported on both architectures, including support for Jumbo Frames, Cisco Discovery Protocol (CDP), NetQueue, and NetFlow.

VMware ESXi is the latest hypervisor architecture from VMware. It has an ultra-thin architecture with no reliance on a general purpose OS, yet still offers all the same functionality and performance of VMware ESX. For a comparision between ESX and ESXi 4.1 see the following article.

What’s the difference between free ESXi and licensed ESXi?

VMware vSphere Hypervisor is the new name for what was formerly known as VMware ESXi Single Server or free ESXi. VMware vSphere Hypervisor is the free edition of the vSphere production line. It is licensed to only unlock the hypervisor functionality of vSphere, but it can be seamlessly upgraded to more advanced offerings of VMware vSphere. VMware vSphere is available in multiple editions including several options specifically designed for small businesses. So if you want to try out VMware virtualization start with the VMware vSphere Hypervisor and if you like what you see you can load a license without reinstalling the hypervisor layer. In the free ESXi edition the different APIs like the storage API are not activated.

How do you manage your free VMware vSphere Hypervisor license?

You can use the free VMware vSphere Client to manage VMware vSphere Hypervisor. With this client you log into each vSphere Hypervisor host individually to manage it via the GUI. You can also use the vSphere Command Line Interface (vCLI) utility to query the host, but beware it is in read only when you use the free ESXi version.

Back in time

VMware ESX Architecture.

In the original ESX architecture, the virtualization kernel (referred to as the vmkernel) is augmented with a management partition known as the console operating system (also known as COS or service console). The primary purpose of the Console OS is to provide a management interface into the host. Various VMware management agents are deployed in the Console OS, along with other infrastructure service agents (e.g. name service, time service, logging, etc). In this architecture, many customers deploy other agents from 3rd parties to provide particular functionality, such as hardware monitoring and system management. Furthermore, individual admin users log into the Console OS to run configuration and diagnostic commands and scripts.

VMware ESXi Architecture[1].

In the ESXi architecture, the Console OS has been removed and all of the VMware agents run directly on the vmkernel. Infrastructure services are provided natively through modules included with the vmkernel. Other authorized 3rd party modules , such as hardware drivers and hardware monitoring components, can run in vmkernel as well. Only modules that have been digitally signed by VMware are allowed on the system, creating a tightly locked-down architecture. Preventing arbitrary code from running on the ESXi host greatly improves the security of the system.

A VMware ESX deployment is circa 2 GB while a VMware ESXi deployment is less than 100MB.

Comparison between ESX and ESXi

VMware ESX

  • VMware agents running in service console (COS)
  • Also almost all other management functionality provided by agents running in the service console (COS)
  • Users have to log into the COS in order to run commands for configuration and diagnostics.

VMware ESXi

  • VMware agents ported to run directly on VMkernel
  • Authorized 3rd party modules can also run in VMkernel for example hardware monitoring and hardware drivers.
  • VMware components and third party components can be updated independently
  • The “dual-image” approach lets you revert back to a prior image if needed.
  • Other capabilities necessary for integration into an enterprise datacenter are provided natively
  • No other arbitrary code is allowed on the system

VMware wants us all to move to the ESXi architecture now that they have finished all APIs and because of because of:

  • Stability
  • Security, less patches are required where 90% of the former patches where for the COS.
  • Reduced footprint to less than 32MB

Functionally, ESXi is equivalent to ESX 4, offering the same levels of performance and scalability. However, the Linux-based service console has been removed, reducing the footprint to less than 32MB of memory. The functionally of the service console is replaced by remote command line interfaces in conjunction with adherence to system management standards. Because ESXi is functionally equivalent to ESX, it supports the entire VMware vSphere 4 suite of products, including VMware Virtual Machine File System, Virtual SMP, vCenter Server, VMotion, VMware Distributed Resource Scheduler, VMware High Availability, VMware Update Manager, and VMware Fault Tolerance.

[1] http://www.vmware.com/files/pdf/ESXi_architecture.pdf