VMware ESXi is the bare-metal hypervisor in the VMware vSphere virtualization platform. As a bare-metal hypervisor for creating and running virtual machines (VMs), VMware ESXi runs on top and accesses the hardware directly without the need to install an operating system. This direct access to hardware allows it to perform better, run faster, and be more scalable than other types of hypervisors. This makes VMware ESXi ideal for use in a large-scale virtual desktop infrastructure (VDI), in conjunction with the other components in the VMware vSphere platform.

VMware ESXi Features

VMware ESXi relies on the VMkernel, which is a microkernel, to run the hardware, guest systems, and service layer making up the VMware virtualization platform. The VMkernel runs the physical hardware and guest VMs, connects directly to the CPU and memory, and uses modules linked via another module to access the hardware’s networking and storage components.

Notable features of VMware ESXi include:

Small size

At just 150 MB, Vmware touts ESXi as the world’s smallest hypervisor. A small footprint often means a reduced attack surface from outside threats, aside from easier maintainability. This also means that ESXi does not need frequent patching up.

Convenient installation

With its small size, faster installation is possible, allowing you to set up your infrastructure at the soonest time possible. You can even boot up ESXi from a USB flash drive.

User-friendly administration tools

ESXi offers a built-in, HTML5-compliant browser for administrative use. Organizations that require automated operations can also utilize the vSphere Command-Line Interface for remote management and application programming interfaces (APIs) based on Representational state transfer (REST).

Secure design

The data that exists in your VMs are secure from prying eyes using built-in encryption. Add role-based access plus extensive logging and auditing capabilities and you get a secure virtual platform at the outset.

Scalable reliability

No matter your application requirements, a single ESXi hypervisor can be configured to run as many as 128 virtual CPUs and 120 devices on 6 TB of memory. ESXi also features a high-performance cluster file system dubbed the Virtual Machine File System (VMFS) that allows more storage resources to be distributed, even with limited physical storage. VMs can also use more than one CPU simultaneously.

Extensive support and compatibility

ESXi’s popularity as an enterprise platform means wide support from hardware vendors and application partners, as well as compatibility with a broad range of applications and guest operating systems.

VMware ESXi Requirements

Due to its small footprint, ESXi can run on a host machine with as few requirements as:

• Two CPU cores
• A single 64-bit x86 processor was released after September 2006
• 4 GB of RAM, a gigabit network adapter, and a 4GB drive

However, for better performance, it is recommended that the host have four or more CPU cores and at least 8 GB of RAM, as well as dual gigabit or faster Ethernet adapters and redundant drives.

If your organization is running 64-bit VMs, you must enable hardware virtualization for the x64 CPUs in the ESXi server. In addition, the no-execute/execute-disable (NX/XD) bits in these CPUs must be enabled in the BIOS. NX stands for Never eXecute and is available in AMD CPUs; eXecute Disable is Intel’s version of the bit. The NX/XD bit reserves memory in the hardware’s data storage areas to prevent them from being hijacked during malicious attacks. Thus, it provides an extra layer of security to an ESXi server.

Other requirements include a Small Computer System Interface (SCSI) disk or a local and non-network, logical-unit-number configured (LUN-configured) Redundant Array of Independent Disks (RAID) with unpartitioned space for hosting the VMs. Serial ATA (SATA) disks are also supported.

ESXi hosts support booting from the Unified Extensible Firmware Interface (UEFI) on hard drives, CD-ROM drives, or USB media. Network booting and provisioning of ESXi hosts with UEFI are also supported. For compatible hardware, ESXi can also boot from disks that are 2 TB or more in size.

To start using ESXi for your virtualization requirements, install it directly on the host machine’s hard disk. Installation is straightforward as well—start the installer and go through the wizard. Post-installation, you can change the host options from the console and launch VMs using the HTML5-based vSphere Client.

VMware ESXi Licensing Model and Cost

VMware ESXi is provided as part of the free vSphere Hypervisor edition. Thus, the tool itself is free to use. However, for easier manageability, you might want to use the vSphere Server, vSphere management tools, and other VMware features with ESXi. This means paying licensing fees on a per-CPU basis, with a license valid for use in up to 32 physical cores. For CPUs with more than 32 physical cores, you need more licenses.

There is also a wide range of vSphere Editions with varying configurations. At the time of writing, the costs of these editions vary as well, with the least expensive costing $510 for three servers and two processors per server, and the most expensive costing $6,545. You need to pay separate fees for Basic Support and Production Support.

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