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foreword
This chapter will explain the virtualization layer architecture of cloud computing and understand the architectural models of the virtualization layer of cloud computing.
1. Virtualization layer architecture
- Virtualization layer architecture: full virtualization, paravirtualization, hardware-assisted virtualization
- KVM -------- "full virtualization
- Xen----------"paravirtualization
- CPU (AMD, Intel) --------------》Hardware Assisted Virtualization
Architecture 1: Full Virtualization
Full virtualization: That is, the abstracted vm has complete physical characteristics, and the virtualization layer is responsible for capturing CPU instructions and acting as a medium for instructions to access hardware.
It uses virtual machines to coordinate guest operating systems and raw hardware. Full virtualization is to fully simulate the underlying hardware details through a virtualization logic layer Hypervisor between the client and the host. Full virtualization means that the entire virtualization is implemented in software.
Typical ones are: VMware, Virtyalbox, virtual PC, KVM-x86
VirtualBox is an open source virtual machine software. Users can install and execute SolarisWindows, DOS, Linux, OS/2Warp, BSD and other systems on VirtualBox as client operating systems.
KVM-x86 is a kernel-based virtual machine (Kernel-based Virtual Machine), which is a kernel module of Linux, which makes Linux a Hypervisor. It supports x86 (32 and 64 bit), s390, Powerpc and other CPUs.
Features:
- OS does not need to be modified.
- The speed and functionality are very good, and it is very simple to use.
- Good portability.
Full virtualization: KVM
KVM (Kernel-Based Virtual Machines) is a virtualization technology based on the Linux kernel, which can directly convert the Linux kernel into a Hypervisor. Therefore, the Linux kernel can directly manage the virtual machine, and directly invoke the memory management and process management subsystems in the Linux kernel to manage the virtual machine.
Composition: It consists of two parts: the KVM module (CPU virtualization, memory virtualization, interface) in the kernel state and the QEMU in the user state.
QWMU completes other virtualization (IO virtualization, network virtualization) through the interface provided by KVM.ko. It is composed of QWMU.
- Part 1: Memory, CPU, Interfaces, Virtualization
- Part II: Other virtualization (IO, etc.)
Architecture 2: Paravirtualization
Paravirtualization: At the beginning of the period, it is to solve the difficulty of low efficiency of full virtualization. It needs to modify the OS, and the work efficiency is much higher than that of full virtualization. The hypervisor is directly installed on the physical machine, and multiple virtual machines run on the hypervisor. The hypervisor implementation is generally a specially customized Linux system.
Typical ones are xen, VMware ESXi, Microsoft Hyper-V
Hyper-V is Microsoft's implementation of a hypervisor. Hyper-V takes the resources of a single host computer and distributes that resource among multiple virtual machines (VMs) running on the same physical hardware. Hyper-V provides each VM with its own space to run its own operating system (OS), which is independent of the host OS and other VMs.
Features:
- The structure is more streamlined
- A slight advantage in overall speed
- The OS needs to be modified, which is troublesome in terms of user experience.
Paravirtualization: Xen
Xen: Directly change the operating system kernel, change the OS into a lightweight Hypervisor, and run a Domain0 that manages all resources for resource scheduling.
Composition: Xen Hypervisor (virtualization layer), Domin0 (management host), Domin U (user virtual machine).
Architecture 3: Hardware Assisted Virtualization
- Hardware-assisted virtualization: With the application of virtualization technology becoming more and more widespread, hardware manufacturers such as Intel and AMD support virtualization technology through hardware transformation.
It is often used to optimize full-virtualization and para-virtualization products, such as VMware Workstation. Although it belongs to full virtualization, it introduced hardware-assisted virtualization technology in version 6.0, such as Intel's VT-x and AMD's AMD-V. Both mainstream full-virtualization and para-virtualization products support hardware-assisted virtualization. (VirtualBox, KVM, Xen, etc.)
2. Comparison of KVM architecture and Xen architecture
KVM (commonly used)
- Support full virtualization
- built into the kernel
- Easy version installation, upgrade and maintenance
- high performance
- Summary: KVM platform architecture focuses on performance
Xen
- Support full virtualization, paravirtualization
- Need to modify the kernel
- With newer versions, Xen needs to recompile the entire kernel
- good isolation
- Summary: Xen platform architecture focuses on security
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