Understanding Virtualization
There are many different types of virtualization occurring in today's computing environment. A simple search for "virtualization" on a popular search engine returns thousands of hits. The list can become exhaustive but it is important to understand what each type does before beginning a large scale IT virtualization project.
Today many virtualization customers and consultants consider 1999 the first year of virtualization with VMware's first release. Though VMware is deeply rooted in many implementations, virtualization is not a new concept. It has its roots with IBM and pseudo machines over 40 years ago. During that time software managed different allocation of resources inside a mainframe architecture which gave birth to the modern day hypervisor. A hypervisor intercepts, schedules, and translates requests from an operating system that is destined for some type of physical hardware like a CPU. The hypervisor also manages these requests going from hardware to the operation system or systems. It is the hypervisor that provides the layer of abstraction that is synonymous with server virtualization but there is more than one type of hypervisor, as we will review later.
Types of Virtualization
There are currently several types of virtualization deployed by IT organizations. They include but are not limited to Hardware (Server), Desktop (Client), Software (Application), Storage, and Network virtualization. One can easily see how difficult it can be to separate the distinct functions of virtualization throughout an organization. When should you target desktop virtualization over server virtualization or maybe your organization needs a mixture of both? Let us begin to dive into each type of virtualization so that you are able to make your own determination.
Hardware (or Server) virtualization
As datacenters begin to bloat causing problems with HVAC, power consumption, and rack space, server virtualization has become more prevalent. Most organization were purchasing commodity server hardware and utilizing only a fragment of the physical capabilities of the servers. Understanding that software had the ability to aggregate this underutilized hardware into a larger pool of resources for multiple operating systems on a single hardware platform, companies like VMware have been able to transform the server virtualization market. Using specially designed software, an administrator can convert one physical server into multiple virtual machines. Each virtual server acts like a unique physical device, capable of running its own operating system (OS). As we discussed earlier the component that makes the separation between the hardware and operating system possible is known as the hypervisor. There are two types of hypervisors that deserve distinction.
Type 1 VS. Type 2 Hypervisors
Type 1 hypervisors are those hypervisors that logically sit between the bare metal server and the operating system. The XEN hypervisor is a good example of this type of system. XEN is the broker between calls to the physical hardware and the operating system.
Type 2 hypervisors are hypervisors that rely on an operating system to host the hypervisor itself. These types of hypervisors actually virtualize the memory management and I/O between multiple virtual machines and the hypervisor host. VirtualBox is a good example of a type 2 hypervisor because the operating system in installed prior to adding the application/hypervisor to the system.
Desktop (or Client) Virtualization
Desktop or client virtualization refers to the concept of separating a person computer from a physical machine in a client-server model. The most common implementation of is known as Virtual Desktop Infrastructure or VDI. In a VDI model, virtual machines are hosted on a centralized server. This centralized server streams an image to a host system allowing the user to access the needed applications or system. Normally, systems are hosted in the datacenter and accessed through Independent Computing Architecture (ICA) Protocol, Remote Desktop Protocol (RDP), or PC-over-IP (PCOIP) protocol but there are a few products that allow images to be streamed directly to user end devices rather than just streaming the visual representation of the PC.
Software (or Application) Virtualization
Software virtualization is a concept used to describe software that improves portability, manageability, and compatibility of applications by abstracting them from their native environment. This abstraction normally occurs through encapsulation or repackaging of the application. Many times this method of virtualization is used for applications that do not support an upgrade to a different operating system.
Storage Virtualization
Storage virtualization is one of the most well known type's virtualization. A storage system normally uses virtualization to present separation of logical and physical storage. This is why systems do not have to directly access disks but rather access logical volumes to provide the most flexibility to users and subsystems throughout the datacenter or at home. The computing would become truly tedious if each user had to address the specific disk address he/she was targeting with data. Instead, physical locations are abstracted away and data can be saved to a logical drive that provides higher levels of protection.
Network Virtualization
Network virtualization provides an innovative approach to running multiple networks on a single physical backbone. These networks are used for entirely different functions and it is for that reason that IT departments want to keep them separate. Imagine experimentation and/or development taking place on the same network that all you are banking transactions are occurring. Would it make you nervous that your customers are depending on a network that is unproven or even worse, not secure? This type of environment is perfect for network virtualization, which can provide a layer 2/3 separation between systems.
Virtualization
As you can see, there are different spans of virtualization that reach across often-blurred lines of computing. In order to understand the keys to success for any project it is important to understand its components. I hope that this brief overview has provided some much-needed insight into the world of virtualization.
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