There are roughly three types of server virtualization technologies: full virtualization, paravirtualization, and operating system layer virtualization.
Virtualization technology, users can dynamically enable virtual servers, also known as virtual machines, each server can actually make the operating system and any application running on it mistakenly believe that the virtual machine is the actual hardware. Running multiple virtual machines can also unleash the full computing potential of physical servers and quickly respond to the changing needs of the data center.
Data center managers today face a wide variety of virtualization solutions, some proprietary and some open source. Let’s take a look at the three types of virtualization:
One: full virtualization
The virtualization approach uses a piece of software called a hypervisor to create an abstraction layer between virtual servers and the underlying hardware. The core-based virtual machine KVM is an open source product for Linux systems.
The hypervisor can capture CPU instructions and act as an intermediary for instructions to access hardware controllers and peripherals. Therefore, full virtualization technology allows almost any operating system to be installed on virtual servers without modification, without them knowing that they are running in a virtualized environment. The main disadvantage is that the hypervisor imposes overhead on the processor.
In a fully virtualized environment, the hypervisor runs on bare hardware and acts as the host operating system; while the virtual server managed by the hypervisor runs the client operating system guest OS.
Two: Paravirtualization
One way to alleviate this burden is to change the guest operating system to think that it is running in a virtual environment and can cooperate with the hypervisor. This method is called para-virtualization.
Xen is an example of an open source paravirtualization technology. Before an operating system can run on a Xen hypervisor as a virtual server, it must undergo certain changes at the core level. Therefore, Xen is suitable for BSD, Linux, Solaris and other open source operating systems, but it is not suitable for virtualizing proprietary operating systems like Windows because they cannot be changed.
The advantage of paravirtualization technology is high performance. A paravirtualized server can work with a hypervisor to be nearly as responsive as a non-virtualized server. The advantages of paravirtualization over full virtualization are so clear that both Microsoft and VMware are developing the technology to complement their respective products.
Three: Operating system layer virtualization
Another way to achieve virtualization is to add virtual server functions at the operating system level. Solaris Container is an example in this regard, and Virtuozzo/OpenVZ is a software solution for Linux.
As far as virtualization at the operating system layer is concerned, there is no separate hypervisor layer. Instead, the host operating system itself is responsible for distributing hardware resources among multiple virtual servers and making those servers independent of each other. One obvious difference is that if OS-level virtualization is used, all virtual servers must run the same operating system but each instance has its own application and user account.
Although the flexibility of OS layer virtualization is relatively low, the native speed performance is relatively high. In addition, because the architecture uses a single, standard operating system on all virtual servers, it is easier to manage than a heterogeneous environment.
Three types of virtualization summary
Each method of virtualization has its own advantages, and which one to choose depends on the specific situation of the user. A group of servers based on the same operating system is ideal for consolidation through the operating system layer.
The paravirtualization technology combines the strengths of the two, and if it is deployed together with a processor that supports virtualization technology, the advantages will be more obvious. It not only provides good performance, but also provides the ability to run multiple heterogeneous client operating systems.
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, follow me for continuous updates!! Among the three methods, full virtualization performance is affected. They are completely isolated from the host operating system. It is ideal for software quality assurance and testing, and also supports the widest variety of client operating systems.
Fully virtualized solutions offer other unique capabilities. For example, they can take "snapshots" of virtual servers to preserve state and facilitate disaster recovery. This virtual server image can be used to rapidly provision new server instances. A growing number of software companies are even offering evaluation versions of their products as downloadable, prepackaged virtual server images.
Just like physical servers, virtual servers require ongoing support and maintenance. The growing popularity of server virtualization has created a thriving market for third-party tools, whether it be physical-to-virtual environment migration utilities or major systems management consoles for virtualization The process of migrating a traditional IT environment to an efficient, cost-effective virtual environment.
Original link: https://zhuanlan.zhihu.com/p/554649395