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The architecture and degree of server virtualization

Also known as a hosted hypervisor architecture, this architecture using a hypervisor layer running on the platform operating system.

use the operating system services are offered to divide the resources to the virtual machine. If we view this hypervisor is a layer of software separately, then the virtual machine's guest operating system will reside on the third layer compared to the server hardware.

I. The virtualization architecture.

1. Hosted virtualization-based architecture.

We can see a system virtualization using the Hosted model-based four layers act as follows:
Hardware platform: includes entry equipment, storage devices (HDD, Ram), CPU processors, and other devices (network equipment, graphics processors, sound ...)
Host operating system: the operating system performs the direct contact with hardware, thereby providing the services and functions through the operating system.
The system virtual machine monitor (hypervisor): running on the Host operating system platform, these systems take resources and services provided by the host operating system, implementation of the management, divided on these resources.
Virtual machine applications: use of resources by the hypervisor Manager.
Liaison between the hardware and device drivers on the operating system in VMM virtual type is described as follows:
The first step in simulating the hardware: Virtualization hypervisor Layer will create a partition on the drive for the virtual machine. This partition including virtual hardware such as disk drives, memory. ...
Hypervisor build liaison between layers with virtualization operating system: When a virtual machine is accessing the resources class hypervisor will replace the virtual machine which sent the request to the host operating system to request made,
When the operating system gets these requirements. It communicates with the hardware device drivers.
The hardware device drivers to communicate to the hardware on the machine.
This process happens in reverse when the answer from the hardware to the operating system.
Some form of hypervisor systems Hosted-base including such as Vmware Server, Microsoft Virtual PC, the Java virtual machine.
2. Hypervisor-based virtualization architecture.
Also known as bare-metal hypervisor architecture. In this model, software hypervisor layer runs directly on the hardware platform of the server, not through any one operating system or any other platform. Thereby, the hypervisor has the ability to control, to control the hardware of the server. At the same time, it also has the ability to manage the operating system running on it. In other words, the operating system will run on a layer above the bare-metal hypervisor formats. The following figure illustrates a more specific for this problem:
We can see a system server virtualization using Bare-metal hypervisor platform consists of three main layers:
Hardware platform: includes entry equipment, storage devices (HDD, Ram), CPU processors, and other devices (network equipment, graphics processors, sound ...)
Platform virtualization layer Virtual Machine Monitor (hypervisor), make contact directly with the underlying hardware platform, management and distribution of resources for the other operating system are located on it.
Virtual machine applications: this virtual machine will take resources from hardware, through the management and allocation of the hypervisor.
When an operating system access or interactive hardware resources on the host operating system, the work of a Hypervisor will be:
Hypervisor hardware simulation. It makes the operating system that you are using the physical resources of the system.
Hypervisor to contact the device driver
The hardware device driver communicates directly with the physical hardware.
Hypervisor model-Base shaped as the Hypervisor and Microkernel Hypervisor Monothic.
Some example of Bare-metal hypervisor systems such as Oracle VM, Vmware ESX Server, IBM's POWER Hypervisor (PowerVM), Microsoft's Hyper-V (released in June 2008), Citrix XenServer ...
A. Monolithic Hypervisor.
Monolithic Hypervisor is a server operating system. It contains the drivers (Driver) in-class Hypervisor hardware operations to access hardware resources below. When the operating system running on the virtual machine to access the hardware through the device driver layer of the hypervisor layer.
This model is highly effective, but like any other solutions besides the face of advantages, it also has downsides. Because in the course of the operation, if the device driver layer hardware is damaged or appears an error then the virtual machine installed on it to the influence and harm. Add to that today's hardware market is very diverse, many types and so many different providers, should the driver of the Hypervisor in this virtualization types will probably not be able to support the active control of the hardware properly and the performance certainly will also not be as expected. A driver cannot control the good operation of all the equipment should it also have hardware devices that do not support. This shows that depends too much on the type of device to restrict the development of this technology.
B. Microkernelized Hypervisor.
Microkernelized Hypervisor is a type of virtualization like Monolithic Hypervisor. Differences between the two types are in the Microkernelized hardware device drivers below are installed on a virtual machine and is called the primary driver, the main driver of this created and manage the driver for the virtual machine. When the virtual machine is in need of contact with hardware, the driver will contact the main drivers and drivers of this primary will move down Hypervisor layer required to communicate with the hardware.
3. Hybrid virtualization architecture.
Hybrid is a newer type of virtualization and has many advantages. Which hypervisor virtualization layer runs parallel with the server operating system. However, in the structure of this virtualization, virtual servers must still go through the host operating system to access your hardware but discrepancies in both the server operating system and virtual server are running in kernel mode. When a server or the operating system in a virtual host need to handle the task, then the CPU will serve the need for the server or virtual server. Why Hyrbird faster virtualization layer is run in kernel mode (run in parallel with the operating system), as opposed to Virtual Machine Monitor virtualization layer running in user mode (run as an application installed on the operating system).

II. The level of virtualization.

1. Full virtualization-Full Virtualization.
This type of virtualization that we don't need to edit guest operating system (guest OS), as well as the software, has been installed on it to run in the host operating system environment (host OS). When a piece of software running on the guest OS, the code it's not damaged that run directly on the host OS and the software as being run on a real system. Besides, full virtualization may experience some problems about performance and effectiveness in the use of system resources.
Virtual machine drivers are provided for the virtual machine a "picture" of the entire system, including virtual BIOS, virtual memory space, and virtual devices. Virtual machine drivers are also required to create and maintain the data structure for virtual components (especially memory), and this structure must always be updated for each of the respective access made by the virtual machine.
2. Paravirtualization
Is a server virtualization method in which, instead of simulating a complete hardware environment, this virtualization software is a thin layer of cornered the access the server operating system on the physical basis of machine resources , use a single kernel to manage Virtual Server and allow them to run at the same time (maybe implied, a Server is the user interface that is used to interact with the operating system).
Parallels virtualization to deliver higher speeds than full virtualization and effective use of resources was also higher. But it requires the guest operating system running on your shirt to be edited. This means that there is not any operating system can also run parallel virtualization (left with full virtualization). Windows 7 's XP Mode is a typical example of Parallels virtualization.
3. Operating system virtualization.
An operating system is operated on an OS Server already exists and has the ability to provide a set of the library to interact with the application, making each application access hardware resources feels like direct access server Physics. From the perspective of the application, it was noticed and interact with applications running on a virtual OS, and interact with a virtual operating system even though it controls the virtual operating system resources. In General, could not find the applications or the operating system resources placed in the virtual operating system.
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