Six major Linux Virtualization Technologies (1)

We have learned about the advantages of Linux virtualization. Currently, the most widely used virtualization operating system is Windows, but the growth speed of Linux is amazing and there is a trend of replacing Windows. Linux virtualization technology can be divided into six different methods. In this article, we will discuss these six methods for implementing Linux virtualization and a variety of virtualization solutions in Linux.

When we discuss virtualization solutions, we often mention specific products of specific vendors, but when we mention Linux virtualization solutions, we are more happy to discuss a wide and diverse open source ecosystem. Linux supports multiple virtualization platforms and extends multiple technologies. It is also an element of a complete solution.

Virtualization-the old tree is blooming

Although virtualization is so popular today, virtualization is not a new technology. IBM has started to deploy virtualization half a century ago. First virtualization technology was tested on IBM M44 computers and then popularized on IBM System/360 mainframe products. The earliest true overall application virtualization hardware platform was the IBM CP-40 system, which was used in commercial applications at the end of the 1960s S.

Virtualization includes multiple layers, such as hardware virtualization, which directly supports the software environment from the underlying hardware platform. The other is operating system virtualization, which is a highlight of Linux.

On the hardware layer, software independent from the operating system is called hypervisor or Virtual Machine monitor. Hypervisor creates a virtualization platform, and operating system instances run on the platform. This allows the hardware platform to be shared by multiple operating systems and applications, thus reducing hardware costs.

The entity running on hypervisor is called a Virtual Machine (VM). It is a "Container" used to hold Operating Systems, Applications, and data elements ". The operating system and application data in the virtual machine are stored in the virtual disk. hypervisor uses the virtual disk to start the virtualization platform. The Virtual Machine is encapsulated as a file, which is better managed than distributed files.

Local virtualization and host virtualization Models

Early virtualization models were called Type 1 or local virtualization native virtualization alization. hypervisor runs on hardware directly and is a virtual machine on the hypervisor. Later, the host virtualization hosted virtualization mode was introduced. Known as Type 2, hypervisor runs on the operating system and allows two or more operating systems to coexist on the same platform.

Linux virtualization technology Basics

After learning some basic knowledge about virtualization, let's start to discuss some knowledge about Linux virtualization. First, it is to simulate Emulation). It is to convert the service of an operating system Host and display it as another operating system Guest). The Host and Guest systems are not necessarily the same, for example, the Host system may be an x86 Platform and can provide simulation for the PowerPC platform, even if the commands and architecture are completely different.

In addition, the hypervisor simulator emulator can provide simulation on multiple platforms. For example, the following example shows that the PowerPC and ARM systems can be simulated on the Host system. The simulation process is not limited to the Type 2 virtualization model. This process exists in virtualization technology.

Simulation process in the virtualization Model

The two most popular Linux simulators emulator) include QEMU and Bochs processors and platform simulators ). The advantage of this solution is that they are very "lightweight" and support running different Guest operating systems on different Host operating systems and platforms. The disadvantage of this solution is that it is inefficient to simulate commands. QEMU allows the kernel and internal user code to be accelerated through the simulation of dynamic encoding conversion. In addition, QEMU is a good embedded platform development tool that can develop and test code for CPUs that are different from the host. QEMU can also be used in other virtualization solutions for device simulation.

Platform Virtualization

A more traditional virtualization solution is platform virtualization or hardware virtualization. It has two main forms: full-virtualization (full-virtualization) and semi-virtualization (para-virtualization ).

Full Virtualization: The virtualization platform uses hypervisor to host Virtual Machine VMS. The key to full virtualization is that these virtual machines, that is, operating systems running on these virtual machines, can run on the hypervisor, this mode is ideal when a real virtual platform is needed, but it has a disadvantage.

In full virtualization, virtual machine VMS treat the virtual platform as a physical platform. The Guest operating system driver working on the virtual platform is like running on real hardware. However, we need to consider what this means. The communication between the Guest operating system and the virtual platform is like that between the real platform. There is another simulation layer in the hypervisor, simulate the hardware platform and Forward Virtual Machine Access to the hardware, as if the virtual machine is directly using the real hardware. This process requires a lot of processing, which limits the I/O performance of the Guest system.

One way to solve this problem is to make the Guest operating system realize that it is virtualized. This form is called semi-virtualization para-virtualization alization). For example, in this mode, the Guest system contains the drivers required to shorten the hardware access process, which frees the Guest system from unnecessary work for higher level work.

Two platform virtualization Methods

Although full virtualization is an ideal solution, modifying the Guest operating system can minimize the processing overhead and greatly improve the performance.