Types of virtualization

There are basically four types of virtualization, Hosted, Binary Translation, Paravirtualization, and Hardware Assist.

• Hosted: This type of virtualization uses a base operating system to run the physical computer and the hypervisor manages access to the physical resources through the operating system. The base operating system is normally Windows or Linux, but there are hosted virtualization versions for the Mac. VMware Virtual Server and Microsoft Virtual Server 2005 are examples of a server-based hypervisor using a hosted design.
• Binary Translation: This type of virtualization has a very thin operating system below the hypervisor. The hypervisor captures all system calls for hardware resources and translates the virtual calls to physical calls. By translating all system calls, each virtual machine is completely isolated from the underlying hardware. VMware ESX server and Microsoft’s Server Core are examples of this type of hypervisor.
• Paravirtualization: This design of hypervisor allows some specific system call to be passed directly to the physical resources. The remaining system calls are still translated before passing to the physical resources. In a true paravirtualization hypervisor, small pieces of the guest operating system are modified to modify the dangerous kernel operations. These changes are picked up by the hypervisor and translated to the physical resources. Some less disruptive hardware calls are allowed to pass directly to the physical resources.
• Hardware Assist: This type of hypervisor leverages the benefits of the paravirtualization design and takes it a step further by adding specific CPU calls from the guest virtual machines. This allows for an even thinner hypervisor and increased performance of the virtual machines. Both Intel VT and AMD-V are examples of hardware assist in a paravirtualized hypervisor. Commercial versions of this type of hypervisor can be found in Citrix XenServer, Microsoft Hyper-V, and VMware ESX 3.5.

Benefits of Virtualization

With the cost of servers remaining basically flat, their power and capabilities are ever increasing. This has created a situation where very little of the power and performance of the physical computers is actually used in running the  process or application that has been tasked on that server. It has been shown by several different studies that most modern servers are only running at 2–20% of their capacity. This is an inefficient use of the resources. Businesses want to get a better value for the money they spend on servers.

One of the key benefits of a virtual infrastructure is that all the virtual machines have standard virtual hardware regardless of the physical platform they are currently running on. This feature creates a utility computing environment where virtual machines simply work on whatever physical server the organization chooses. A hypervisor is simply a program that allows multiple operating systems to share a single physical host. Leveraging the advanced features of many hypervisors, an administrator can move running virtual machines to other physical servers without interruption to the users accessing the virtual server. The old physical server can be upgraded, repaired, or replaced, all without changing the virtual machine.

This utility computing feature allows for rapid recovery in case of disaster or security breach in that the virtual server configuration files and virtual disks can be copied or snapshots taken and transferred to a remote facility or separate storage and then used to restart the virtual machine in a different location without regard to drives or physical hardware differences. This feature allows for recovery of virtual machines in minutes instead of hours or days using traditional servers.

There are other side-expenses to consider when determining the value of  virtualization, such as the cost of network ports, power connections, heating and cooling, space requirements, maintenance and upgrades, replacement and disposal of equipment, and the amount of manpower it takes to manage and maintain a physical infrastructure. For the organization, the benefits can be:

1. Reduced cost of hardware
2. Reduced space requirements
3. Rapid deployment of new servers
4. High availability
5. Hosting multiple environments
6. Separation of virtual
7. Ability to maintain a Test/Development Environment in an easy fashion
8. Lower costs for software testing

The purpose of Virtualization

Virtualization is the ability to allow one physical computer to run multiple instances of an operating system or multiple operating systems on the same physical computer. The basic concepts of virtualization are not new but come from the mainframe computing world, where they were originally designed to maximize the resource utilization of expensive hardware and software so businesses could get the best most efficient utilization of their mainframe processing capacity. This ability of the more modern servers also presents both security challenges and benefits. With more virtual machines there are more patches that need to be applied, more servers to be secured, virtual machines to be created and just as important removed, and users accessing both internal and external resources.

In addition to server virtualization there is application virtualization technology. Virtual applications run on servers located remote from the users. These users do not need to have the application or data loaded on their desktop devices. Application virtualization allows applications that may be sensitive or not compatible with a user’s desktop to operate as if they were loaded locally. These virtual applications also do not leave a trace on the client machine, so they are safe to use from computers outside the trusted network.