Vcenter Server - Basics

In the previous blog, we were talking about Server Virtualization, which allows us to run multiple Virtual Machines on it. Total number of Virtual Machines which can run on a single Physical Server depends on size of the Virtual Machine and Physical resources (CPU and Memory) on the Physical Server. If the Physical Server goes down, that will fail all the running Virtual Machines.

Even I have seen some customers who just Install ESXi and run plenty of critical Virtual Servers on it and say they are on Virtualization. I tell them, they are on Virtualization but with risk!!! If the physical server fails, they will lose access to Running Virtual Machine. Just Virtualizing is like utilizing 10% benefits of Virtualization. Now, to address these multiple Virtual Machines Failure, there is Management software called vCenter Server.

vCenter Server is installed on Windows Server Operating system like server 2008 R2 and it manages all the hosts and Virtual Machines from one place. It is just not used for managing all the Virtualized Servers and hosts, it provides various distributed Services like vMotion, HA, DRS, FT etc.

People who do not like vCenter Server on Windows, they can deploy vCenter Server Appliance (SUSE Linux based), it is preconfigured with Database and Services like Single Sign On, Inventory services. There is no difference in functionality just that one is running on Windows platform and other on Linux.

A database is mandatory for vCenter Server, the embedded Database which comes with vCenter Server is suitable for 5 Hosts and 50 Virtual Machines on Windows Platform and for vCenter Server Appliance (vCSA 5.5) it supports upto 500 Hosts and 5000 Virtual Machines, for any environment bigger than 5 Hosts and 50 Virtual Machines, a full blown Database is mandatory.

I will talk about all the distributed feature what vCenter Server provides in next blogs and watch out for lab section for deployment of ESXi 5.5 and vCenter Server Appliance 5.5. There is lot to understand about vCenter Server and how it interacts with ESXi hosts and Virtual Machines, which I will cover in other blog. 

What is Virtualization

I just added new section to my blog where I will try to cover concepts of various Vmware products, their architecture and how the product works. I will start from Vmware Hypervisor and then to more complex products like vCloud Director, so that anyone who is new to Virtualization can also get an idea about how exactly Virtualization works. So, let's start with Vmware hypervisor

Before we get into Virtualization, let me brief you about Vmware offering. There are two types of Virtualizations

1. Hosted Virtualization
2. Datacenter / Bare-Metal Virtualization

Hosted Virtualization: Here you are running Virtual Machines on top of regular Operating System, like Windows Vista, Windows 7 / 8 etc. So, a software is installed on normal operating system and with help of that software, VMs can be created and most of the product features can be experienced. Vmware has a product called "Vmware Workstation 10" for Windows and Fusion 6 for Mac Desktops. This is how Workstation looks with some Virtual Machines on it. Very simple and very useful for Lab and Demo purpose.

Datacenter / Bare-Metal Virtualization: You can say it is the Hypervisor layer or Operating System which is directly installed on the physical server and runs the Virtual Machines directly on top of it. Even physical machines can be converted to Virtual Machines with the help of software (like Vmware Converter) and run on this hypervisor. These Virtual Machines are same as Physical Machines but with more capabilities and more flexibilities. Many devices like Hard Drive, CD/DVD, Floppy devices can be added on fly. Also, Memory and CPU can be hot-added by enabling that feature.

Now, let's understand what exactly is Virtualization:

"It's an abstraction layer that masks the physical resources of hardware equipment to provide a system with resources that differ from what they actually are."

Normally when you install any operating system (like Server 2008 R2) on a physical server, all the physical resources are restricted to the same operating system and it is not fully utilized, you can always see there is lot of idle resource like CPU 12% utilized, but rest of 88% CPU is idle. Of course this would be used during spike but the spikes happen for limited time.

When you install Vmware ESXi (Hypervisor from Vmware), it masks the physical resources (cpu, memory) and provides new level of independence, where the resources can be distributed to multiple Virtual Machines. Below picture shows you the difference between Traditional server and a Virtualized server. All the Virtual Machines are getting the CPU, RAM, Network from the physical server and they are Virtual CPU (vCPU), Virtual RAM and Virtual Nic.

• Single physical server runs multiple Virtual Machines.
• Each Virtual Machine has its own applications running.
• Any Operating System can installed in a Virtual Machine.
• Virtual Machines can of different sizes, i.e., different configurations.

Server Consolidation is the major reason why companies Virtualize their environment. Multiple Servers can run as Virtual Machines on a single bigger physical server after installing Vmware ESXi on it.

I hope this was helpful to understand the definition of Virtualization. Before I end this introduction blog, I will leave you with one question, what happens if the physical server goes down due to some hardware failure, will it not fail all the Virtual Machines running on it ?