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Today, i want to discuss about Virtualization, my most favorite thing in my work place. I am a big fan of VMware, as they are the Virtualization leaders in the industry. The concept of virtualization is itself beyond the imagination. As of we all are known about software and hardware, those are the big guys up to now. And both are inter dependable on one another. One not works without the other. For example, if you take an operating system, it runs on hardware. Without the hardware, the OS and Applications installed on it will not work. In the same way, if the software (drivers) is not installed the hardware also not work. And as these are inter dependable, there are so many limitations to achieve our needs. So lets see how a common computer architecture looks like.
 
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Normal Computer Hardware Architecture (Overview)
The first layer is hardware layer which is a bare metal, the second layer is Operating system and the third layer is Application Layer. In other words, Operating system will be installed on Hardware and it takes the advantage of the kernel to communicate with hardware. Applications will be installed on the Operating system. like yahoo messenger, vmware workstation, photo shop etc.
Limitations
So as the OS and Applications are dependent on Hardware, if anything goes wrong with the hardware both will get crashed. And with this type of architecture we cannot run multiple operating systems at a time, we can install multiple OS’es but we cannot run them at a time, if we want Linux, we need to logoff from Windows and vice versa. And one more thing is, as per the case studies done by so many professionals, at a point of peek time also, an operating system does not utilize more than 50% of the total physical resources (applicable to servers), so with this we are wasting our money for servers.  That being said, to overcome these limitation  we need is a better solution. Here i want to introduce the hero of Virtualization, that is none other than “VMWARE”.
image May be some of you are already aware and using VMware Workstation Application. If you ask a question like “What is the use of VMware Workstation then? “. Even though it may fulfill some requirements of virtualization and overcome some limitations of normal architecture and it is also providing access to virtual machines w but before that remember its an application which resided on Operating system, that means it provides virtual machines side by side but access to all the resources allocated for those virtual machines are given  by the Operating system only.
What is a Hypervisor?
There are two types of virtualization software's available from vmware. One works at application level (ex. vmware workstation & vmware server) and the other one works at Operating system level (ex.VMWare ESX server, Microsoft Hype-V, Citrix XenServer etc. These are called Hypervisors. The Hypervisor is an operating system/virtualization which directly communicate with the hardware and provides better access of resources to the virtual machines. Where as i said before, virtualization apps like vmware workstation, microsoft virtual server, vmware server will provide access of resources to virtual machines through Operating system, as those are dependent on OS and are residing at application level. So, with the help hypervisor we can take the advantage of extra-ordinary resource allocation and management. With the Hypervisor, the architecture looks like below
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In detail..
1. Hardware – CPU, Memory, NIC and Disk
2. Virtualization Layer– VMware ESX Server Kernel
3. Service Console – VMware ESX Server Operating system (RedHat Based)
4. Virtual Hardware – Set of files, which resembles hardware in the Guest OS
5. Operating System – OS which is installed on a Virtual Machine
6. Virtual Machine – The combination of Virtual Hardware and Operating system (point 4+ 5).
Advantages of Virtualization

1. Utilizing server resources at fullest (by installing virtual machines side by side)
    If  a physical server has 100% resources for example, in the normal architecture at the peek time also the operating system is able to utilize its resources between 25%-50%. In that case, we are wasting the other 50%-75% resources. But with the use of virtualization using a Hypervisor we are creating more than virtual machines. They all are running side by side, they have their own allocated resources. So if you assume like, we have created 2 virtual machines(one windows & one linux) with 50-50 resources allocated for them, and in this case, we are utilizing 100% resources of the server.
2. Access to multiple operating systems simultaneously
3. We are using one physical server, to host one or more virtual machines (depending on the physical server resources). With this we are saving power, data center space and administrative personnel.
4. With the advantage of the features provided by vmware (vmotion, ha, drs, dpm) , we can get uptime of a operating system / application up to 99% .
5. As the virtual machine is made with a set of files, we can move it / copy it / back up it/ restore it very easily. So the administration of machine when compared to physical is very very less. 

Also read this article VMware – Virtual Networking

Besides VMware, there are lot of virtualization products available in the industry. Everyone has their own feature set and specialties. Microsoft Hyper-V and Citrix Xenserver are the other leading virtualization technologies in the industry.

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