ESX vs. ESXi

Author: John Hales, Global Knowledge Instructor, VCP, VCI, A+, Network+, MCSE, MCDBA, MCT, EMCSA

Abstract

VMWare has announced that ESX 4.1 will be the last major version to ESX with the service console. This white paper reviews briefly the history of the service console, the differences between ESX and ESXi, methods to manage ESX and ESXi, and how to modify existing scripts for use with ESXi.

Sample

Introduction

With the recent statement from VMware that ESX 4.1 will be the last major version of ESX with the service console included, many are starting to look toward the future and the role of ESXi in their infrastructures. This white paper will review the following topics:

• A brief history of the service console and its purpose
• The differences in features between ESX and ESXi, with an emphasis on ESX and ESXi 4.1
• The architectural differences between ESX and ESXi
• Methods to manage both ESX and ESXi, including the DCUI (Direct Console User Interface)
• Modifying existing scripts for use with ESXi, including the role of PowerCLI, the VMA, and the vCLI

With VMware's announcement that we will all be moving to ESXi, knowing how to begin and manage the transition process is important.

Brief History of the Service Console and its Purpose

When ESX was first introduced (in 2001) and in version 2, Linux booted 1st, and when it finished, it loaded a script that loaded the VMkernel, and then turned the running of the server over to VMkernel with Linux running in parallel with it, though receiving most resources (including CPU and network, but not memory or disk) through the VMkernel. As of ESX 3, the VMkernel is loaded via the standard Linux initrd process and thus loads earlier in the boot process. In vSphere, the VMkernel loads and then loads the service console, which is actually a virtual disk (esxconsole.vmdk). The service console provides a simple way to load the VMkernel and also provides a place for management agents, backup agents, and system management tasks to run. On the other hand, many of the patches from VMware are not actually for the VMkernel, but rather for Linux.

The service console is based on Red Hat 7.2 for ESX 2.x, Enterprise Linux (RHEL) 3 for 3.x, and RHEL 5 for 4.0 and 4.1. Note that it is not the standard Linux kernel, but rather a customized version built for this specific purpose.

The service console, apart from running the agents and handling some of the management tasks previously described, is a convenient interface into ESX itself. This is why many hardware and software vendors, as well as many system administrators, really like the idea of a console they can log into when problems are encountered. This has been an issue with ESXi, which does not have the service console, so VMware has modified the design of ESXi somewhat in 4.1 to allow both local and remote access to a command prompt (which is not the traditional service console, but many of the commands are the same or similar). They have also worked with the hardware and software vendors to make it easier to install (and update) various drivers and components needed, as well as building more into ESXi itself to reduce the need for those external components.

Differences in Features between ESX and ESXi

The most obvious and basic difference between the two is that ESX has a service console, whereas ESXi does not. IN ESXi 3.5 the first version of ESXi), there were many things that ESX could do that ESXi could not; ESX 4.0 has narrowed the gap, and 4.1 makes the differences almost nonexistent. For example, in 4.0, boot from SAN was supported for ESX, but not ESXi. On the other hand, ESXi can be preinstalled by hardware manufacturers (in a version known as ESXi Embedded) on an internal USB or flash device, meaning all that needs to be done is simple server setup and cabling, and the box can be managed in the existing environment within a few minutes. Note that ESXi Installable is also available, allowing administrators to download and install the OS on either local or SAN storage.

By removing the service console, ESXi is much smaller (it comes on a CD vs. a DVD for ESX in vSphere) and prevents a smaller attack surface in terms of outside hackers trying to gain entry. In addition, there is an entry-level version of ESXi, which VMware calls vSphere Hypervisor, that is completely free (though it has some significant restrictions and cannot be managed via vCenter without a license).

The question is often asked, "Should I choose ESX or ESXi?" As of 4.1, VMware recommends ESXi for all new deployments and to begin the process of migrating to ESXi now for existing deployments. Note, however, that ESX has a larger list of compatible systems than ESXi (though the gap is narrowing all of the time)

Related Courses

VMware vSphere: Install, Configure, Manage [V4.1]
VMware vSphere: Troubleshooting [V4x]
VMware vSphere: Transition to ESXi [V4x]
VMware vSphere: Automation with vSphere PowerCLI [V4x]