What are vSphere, vCenter and ESXi?

What do these terms mean?

When I became an IT professional, terms like vSphere, vCenter and ESXi used to be incredibly confusing for me. I always thought — what do these terms mean in the “Virtual World” of VMware?

I am sure, I was not the only one and there are many more people who are still confused!

Hence, I am hopeful that this post will end this confusion and increase our understanding of Cloud Computing and VMware technology.

VMware

VMware is an American software company that creates virtualization software and provides cloud computing services.

ESXi and Workstation PRO are Hypervisors made by VMware. While vSphere and vCenter are management tools created by VMware to administer ESXi hypervisors.

Hypervisor

Hypervisor is a software that runs and manages Virtual Machines.

There are two types of hypervisors:

Type 1 Hypervisor:

• This type of hypervisor is there purely for running VMs, it does not need another OS to run its VMs. It is installed and runs on bare metal hardware— (a computer without an OS like Windows, Linux, Mac, etc). This type of hypervisor is a stand-alone system that does not need another OS to help manage its VMs.
• An ESXi is a type 1 hypervisor.

Type 2 Hypervisors:

• This type of hypervisor runs on a host operating system such as Windows, Mac or Linux etc. The host OS provides visualization services, such as I/O device support and memory management. A type 2 hypervisor “sits” on top of another OS and uses its resources to manage its VMs.
• Workstation PRO is a type 2 hypervisor.

ESXi

This is a Type 1 hypervisor — it’s a software that is installed on bare metal hardware. It is this ESXi hypervisor that allows one to create and run multiple VMs on a large server with huge amounts of resources

vSphere

vSphere is a management interface that allows users to manage VMs. vSphere is accessed via a web browser with the IP address of the ESXi host.

Diagram of ESXi Host and VMs

The machine on the left has too many resources for one computer to use, so if we install an ESXi on top of it, we can create different VMs, and use its resources to the fullest.

These VMs will use portions of the large server’s resources. To access each host, you will type its IP into the web browser and access it from there. The drawback is that you can only access one host at a time with vSphere.

vCenter

vCenter manages different ESXi hosts, their resources, networking, memory etc — all on one platform. It is a central management interface to manage all of your ESXi hosts and VMs.

It comes with an array of advanced features that allow many different actions such as VM cloning, vMotion, High Availability, Fault tolerance DRS etc. vCenter appliance normally sits on top of an ESXi host as a VM.

Once it is up and running — ESXi hosts are added to the inventory of the vCenter appliance. When this is done, vCenter automatically starts picking up all the VMs in ESXi hosts and can detect all the changes that may happen in these hosts.

Features of vCenter

vMotion

vMotion enables the movement of one VM from one ESXi host to another.

VM Cloning

VM Cloning tool creates an identical VM on the ESXi host.

High Availability

If a Virtual Machine malfunctions, another VM is created to take over the workload of the malfunctioned VM. High Availability minimizes interruptions to an ongoing operation.

Fault Tolerance

If a Virtual Machine malfunctions, other VMs make sure that the workload does not stop while the malfunctioned VM is removed and swapped for a brand new VM. Fault Tolerance prevents any interruption to the operation.

DRS- Distributed Resource Scheduler

DRS spreads the virtual machine workloads across vSphere hosts inside a cluster and monitors available resources for you.

Workstation Pro

This is a type two hypervisor, you can install it on your personal computer, and create VMs within the workstation pro application. Your local OS will provide the necessary resources like memory management, disk space and processing power for the virtual machines.

This is what vCenter, vSphere and ESXi mean. I am hopeful my explanations solved any confusion about these terms in your mind.