| Developer(s) | VMware, Inc. |
|---|---|
| Stable release | |
| Platform | IA-32 (discontinued in 4.0 onwards),[1]x86-64 |
| Type | Hypervisor |
| License | Proprietary |
| Website | vmware.com/products/esxi-and-esx/ |
VMware ESXi (formerly ESX) is an enterprise-class, type-1hypervisor developed by VMware for deploying and servingvirtual computers. As a type-1 hypervisor, ESXi is not a software application that is installed on an operating system (OS); instead, it includes and integrates vital OS components, such as a kernel.[2]
After version 4.1 (released in 2010), VMware renamed ESX to ESXi. ESXi replaces Service Console (a rudimentary operating system) with a more closely integrated OS. ESX/ESXi is the primary component in the VMware Infrastructuresoftware suite.[3]
The name ESX originated as an abbreviation of Elastic Sky X.[4][5] In September 2004, the replacement for ESX was internally called VMvisor, but later changed to ESXi (as the 'i' in ESXi stood for 'integrated').[6][7]
ESX runs on bare metal (without running an operating system)[8] unlike other VMware products.[9] It includes its own kernel: A Linux kernel is started first,[10] and is then used to load a variety of specialized virtualization components, including ESX, which is otherwise known as the vmkernel component.[11] The Linux kernel is the primary virtual machine; it is invoked by the service console. At normal run-time, the vmkernel is running on the bare computer, and the Linux-based service console runs as the first virtual machine. VMware dropped development of ESX at version 4.1, and now uses ESXi, which does not include a Linux kernel.[12]
The vmkernel is a microkernel[13] with three interfaces: hardware, guest systems, and the service console (Console OS).
The vmkernel handles CPU and memory directly, using scan-before-execution (SBE) to handle special or privileged CPU instructions[14][15]and the SRAT (system resource allocation table) to track allocated memory.[16]
Access to other hardware (such as network or storage devices) takes place using modules. At least some of the modules derive from modules used in the Linux kernel. To access these modules, an additional module called vmklinux implements the Linux module interface. According to the README file, 'This module contains the Linux emulation layer used by the vmkernel.'[17]
The vmkernel uses the device drivers:[17]
These drivers mostly equate to those described in VMware's hardware compatibility list.[18] All these modules fall under the GPL. Programmers have adapted them to run with the vmkernel: VMware Inc has changed the module-loading and some other minor things.[17]
In ESX (and not ESXi), the Service Console is a vestigial general purpose operating system most significantly used as bootstrap for the VMware kernel, vmkernel, and secondarily used as a management interface. Both of these Console Operating System functions are being deprecated from version 5.0, as VMware migrates exclusively to the ESXi model.[19]The Service Console, for all intents and purposes, is the operating system used to interact with VMware ESX and the virtual machines that run on the server.
In the event of a hardware error, the vmkernel can catch a Machine Check Exception.[20] This results in an error message displayed on a purple diagnostic screen. This is colloquially known as a purple diagnostic screen, or purple screen of death (PSoD, cf. Blue Screen of Death (BSoD)).
Upon displaying a purple diagnostic screen, the vmkernel writes debug information to the core dump partition. This information, together with the error codes displayed on the purple diagnostic screen can be used by VMware support to determine the cause of the problem.
VMware ESX is available in two main types: ESX and ESXi, although since version 5 only ESXi is continued.
ESX and ESXi before version 5.0 do not support Windows 8/Windows 2012. These Microsoft operating systems can only run on ESXi 5.x or later.[21]
VMware ESXi, a smaller-footprint version of ESX, does not include the ESX Service Console. It is available - without the need to purchase a vCenter license - as a free download from VMware, with some features disabled.[22][23][24]
ESXi apparently stands for 'ESX integrated'.[25]
VMware ESXi originated as a compact version of VMware ESX that allowed for a smaller 32 MB disk footprint on the host. With a simple configuration console for mostly network configuration and remote based VMware Infrastructure Client Interface, this allows for more resources to be dedicated to the guest environments.
Two variations of ESXi exist:
The same media can be used to install either of these variations depending on the size of the target media.[26] One can upgrade ESXi to VMware Infrastructure 3[27]or to VMware vSphere 4.0 ESXi.
Originally named VMware ESX Server ESXi edition, through several revisions the ESXi product finally became VMware ESXi 3. New editions then followed: ESXi 3.5, ESXi 4, ESXi 5 and (as of 2015) ESXi 6.
VMware has been sued by Christoph Hellwig, a Linux kernel developer, for GPL license violations. It was alleged that VMware had misappropriated portions of the Linux kernel,[28] and used them without permission. The lawsuit was dismissed by the court in July 2016[29] and Hellwig announced he would file an appeal.[30]
The appeal was decided February 2019 and again dismissed by German court, on the basis of not meeting 'procedural requirements for the burden of proof of the plaintiff'.[31]
The following products operate in conjunction with ESX:
Network-connectivity between ESX hosts and the VMs running on it relies on virtual NICs (inside the VM) and virtual switches. The latter exists in two versions: the 'standard' vSwitch allowing several VMs on a single ESX host to share a physical NIC and the 'distributed vSwitch' where the vSwitches on different ESX hosts together form one logical switch. Cisco offers in their Cisco Nexus product-line the Nexus 1000v, an advanced version of the standard distributed vSwitch. A Nexus 1000v consists of two parts: a supervisor module (VSM) and on each ESX host a virtual ethernet module (VEM). The VSM runs as a virtual appliance within the ESX cluster or on dedicated hardware (Nexus 1010 series) and the VEM runs as module on each host and replaces a standard dvS (distributed virtual switch) from VMware.Configuration of the switch is done on the VSM using the standard NX-OSCLI. It offers capabilities to create standard port-profiles which can then be assigned to virtual machines using vCenter.
There are several differences between the standard dvS and the N1000v; one is that the Cisco switch generally has full support for network technologies such as LACP link aggregation or that the VMware switch supports new features such as routing based on physical NIC load. However the main difference lies in the architecture: Nexus 1000v is working in the same way as a physical Ethernet switch does while dvS is relying on information from ESX. This has consequences for example in scalability where the Kappa limit for a N1000v is 2048 virtual ports against 60000 for a dvS. The Nexus1000v is developed in co-operation between Cisco and VMware and uses the API of the dvS[36]
Because VMware ESX is a leader in the server-virtualisation market,[37] software and hardware vendors offer a range of tools to integrate their products or services with ESX. Examples are the products from Veeam Software with backup and management applications[38] and a plugin to monitor and manage ESX using HP OpenView,[39]Quest Software with a range of management and backup-applications and most major backup-solution providers have plugins or modules for ESX. Using Microsoft Operations Manager (SCOM) 2007/2012 with a Bridgeways ESX management pack gives you a realtime ESX datacenter health view.
Also hardware-vendors such as HP and Dell include tools to support the use of ESX(i) on their hardware platforms. An example is the ESX module for Dell's OpenManage management platform.[40]
VMware has added a Web Client[41] since v5 but it will work on vCenter only and does not contain all features.[42] vEMan[43] is a Linux application which is trying to fill that gap. These are just a few examples: there are numerous 3rd party products to manage, monitor or backup ESX infrastructures and the VMs running on them.[44]
Known limitations of VMware ESXi, as of April 2015, include the following:
Some maximums in ESXi Server 6.5 may influence the design of data centers:[45]
In terms of performance, virtualization imposes a cost in the additional work the CPU has to perform to virtualize the underlying hardware. Instructions that perform this extra work, and other activities that require virtualization, tend to lie in operating system calls. In an unmodified operating system, OS calls introduce the greatest portion of virtualization 'overhead'.[citation needed]
Paravirtualization or other virtualization techniques may help with these issues. VMware developed the Virtual Machine Interface for this purpose, and selected operating systems currently support this. A comparison between full virtualization and paravirtualization for the ESX Server[46] shows that in some cases paravirtualization is much faster.
When using the advanced and extended network capabilities by using the Cisco Nexus 1000v distributed virtual switch the following network-related limitations apply:[36]
Regardless of the type of virtual SCSI adapter used, there are these limitations:[45]
SRAT (system resource allocation table) – table that keeps track of memory allocated to a virtual machine.
Apparently, the 'i' in ESXi stands for Integrated, probably coming from the fact that this version of ESX can be embedded in a small bit of flash memory on the server hardware.