Virtualization Type
Full virtualization (Full Virtualization)
Full virtualization has become the original virtualization technology, this model uses a virtual machine guest operating system coordination and the original hardware, VMM for coordination between the guest operating systems and the bare hardware, some of the instructions must be protected by the Hypervisor (Hypervisor ) to capture process.
1 full virtualization model diagram
Full virtualization runs faster than hardware emulation, but performance is not as good as bare metal, because Hypervisor need to take up some resources
Paravirtualization (Para Virtualization)
Paravirtualization another similar full virtualization technology that uses the underlying access Hypervisor share hardware, but its guest operating system incorporates source virtualization aspect. The method does not require recompilation or cause a trap, because the operating system itself can be a very good collaboration and virtual processes.
Figure 2 paravirtualization model
Paravirtualized guest operating systems need to make some changes, the guest operating system realize that they are in a virtual environment, but paravirtualization with the original operating system provides similar performance.
Virtualization technology
KVM (Kernel-based Virtual Machine) Kernel-based Virtual Machine
KVM is integrated into the Linux kernel Hypervisor, it is the X86 architecture and hardware support for virtualization technology (Intel VT or AMD-V) is a full Linux virtualization solutions. It is a small module for Linux, use Linux to do a lot of things, such as task scheduling, memory management hardware to interact with the equipment.
Figure 3 KVM virtualization platform architecture
Xen
Xen is a first class hypervisor on bare metal re-run (Hypervisor large column virtualization, KVM, Xen, Qemu of difference ). It supports full virtualization and paravirtualization, Xen support hypervisor and virtual machines communicate with each other, and available on all versions of Linux free products, including Red Hat Enterprise Linux and SUSE Linux Enterprise Server. The most important advantage of Xen paravirtualization, in addition to unmodified operating system can be run directly on xen (such as Windows), allows a virtual machine to run efficiently without the need for emulation, virtual function perceived hypervisor, without We need to simulate virtual hardware, which can achieve high performance.
Figure 4 Xen virtualization platform architecture
QEMU
QEMU is a set of free software simulation processor by Fabrice Bellard written. It Bochs, PearPC similar, but having both do not have some of the properties, characteristics such as high speed and the cross-platform. Kqemu via this open source accelerator, QEMU able to simulate realistic computer speed.
The relationship between the KVM and QEMU
Precisely, KVM is a Linux kernel module is. You can use the command modprobe to load the KVM modules. After loading the module, in order to further create a virtual machine by other tools. But only KVM module is not enough, because the user can not directly control the kernel module to do something, you must also have a job to run in user space tools. The user-space tools, kvm developers have chosen the open-source QEMU virtualization software already formed. Speaking is a QEMU virtualization software. It is characterized by different available virtual CPU. For example, on an x86 CPU can be a Power of virtual CPU, and can use it to compile a program can be run on the Power. KVM QEMU uses part of, and slightly modified, it becomes a controllable KVM user space tool. So you will see, KVM download the official offer has two major components (qemu and kvm) three files (KVM module, QEMU tools and two collection). In other words, you can upgrade only KVM module, you can upgrade only QEMU tools. This is the relationship between the KVM and QEMU.
Figure 5 KVM and QEMU relations