Virtualization, cloud computing, open source code, and more

Borrow http://www.aliyun.com/zixun/aggregation/9847.html "> the opportunity of the national Day holiday to write this long article, comprehensively collated the individual from virtualization to cloud computing at all levels of view. The main content involves virtualization, virtualization management, data center virtualization, cloud computing, public and private cloud, and open source. The entire content of this article belongs to the author's personal opinion, but does not represent any company's viewpoint. Welcome to the discussion.

A, Virtualization

Virtualization refers to the ability to simulate multiple virtual machines on the same physical machine. Each virtual machine has a separate processor, memory, hard disk, and network interface logically. The use of virtualization technology can improve the utilization of hardware resources, so that multiple applications can run on the same physical machine with each other isolated operating environment.

There are also different levels of virtualization, such as virtualization at the hardware level and virtualization at the software level. Hardware virtualization refers to the simulation of hardware to obtain a similar to the real computer environment, you can run a complete operating system. At the level of hardware virtualization, there is full virtualization (fully virtualized, almost complete simulation of a real 11585.html "> Hardware device.) Most operating systems run directly in a fully virtualized environment without any modification. , Partial Virtualization (partial virtualization, only provides simulations of critical computing components or instruction sets.) The operating system may need to make some modifications to run in a partial virtualized environment. and paravirtualization (semi-virtualization, does not simulate hardware devices, virtual machines have an independent operating environment, through virtual machine management program to share the underlying hardware resources. Most operating systems need to be modified to run in a virtualized environment. ) and other implementation methods. Software level virtualization, often refers to the same operating system instance on the basis of the provision of multiple isolated virtual operating environment, but also often referred to as container technology.

At the level of hardware virtualization, modern virtualization technology is often a hybrid of full virtualization and semi virtualization. Common virtualization technologies such as VMware, Xen, and KVM provide support for both full virtualization and semi virtualization. Virtual machines provided in the form of hardware virtualization typically run a complete operating system, with a large number of identical or similar processes and memory pages on the same host, leading to significant performance losses. At present, the memory pages containing the same content can be identified and merged by KSM Technology, but there is no effective means to optimize the processing of the same or similar processes. As a result, hardware virtualization is often called heavyweight virtualization, and the number of virtual machines that can run concurrently on the same host computer is quite limited. At the level of software virtualization, all virtual machines on the same host share the same operating system instance, and there is no performance loss due to running multiple operating system instances. As a result, software virtualization is often referred to as lightweight virtualization, and the number of virtual running environments that can run concurrently on the same host is relatively loose. Taking container on the Solaris operating system as an example, an instance of a Solaris operating system can theoretically support up to 8,000 container (the number of container that can actually be run depends on system resources and load). Similarly, LXC on a Linux operating system can easily support a significant number of virtual running environments on the same host.

In the field of virtualization, domestic companies have a large interest in hardware virtualization, and in the research and production environment, the hardware virtualization technology is mostly adopted. Taobao is the early domestic research and application of software virtualization technology, their experience in the main Taobao site shows that using Cgroup to replace Xen can improve resource utilization. As to whether hardware virtualization or software virtualization should be selected in a real-world scenario, focus should be given to the end user's need to have full control over the operating system (for example, upgrading the kernel version). Software virtualization can be more cost-effective if end users only need control over the running environment (such as the various app engine services at the PAAs level). Software virtualization is also a good choice for applications that provide horizontal scalability for the same application.

For technicians who need insight into virtualization technology, VMware's White paper "Understanding full virtualization, paravirtualization, and hardware Assist" is a good reference.

Generally speaking, the number of users who can directly use virtualization technology is relatively small. In the case of Linux operating systems, users who are able to perform virtual machine lifecycle management are generally those who have access to libvirt permissions. In a company or other entity, these users are usually system administrators.

(Responsible editor: Duqing first)