[虚拟] Hypervisor

[virtualization] Hypervisor

What is hypervisor?

??? A virtualization platform.

??? － Enables you to run multiple operating systems on host computer(注1).

??? － Provide isolated execution environments for each virtual machine.

??? － Manage access between the guest operating systems(注2) running in virtual machines and the

??????? underlying hardware resources on host computer.

??? 注1：host computer 是指用来运行Hypervisor的电脑。??

??? 注2：guest operating systems 是指在Hypervisor上面运行的操作系统。

What is Type1 hypervisor?

??? Type 1 hypervisors run directly on bare metal instead of within an operating system environment.

??? － Provide the best performance,availability,and security of any form of hypervisor.

??? － Example：Microsoft Hyper-V、Citrix XenServer、VMware ESX Server.

??? － 从下图就可以很清楚的看出，

???????? Type 1 hypervisors是直接执行在电脑硬件上，

???????? 而不是在实例电脑的操作系统中，

???????? 使得它的性能、可用性及安全性都会比较好。

What is Type2 hypervisor?

??? Type 2 hypervisors run within an operating system environment running on the host computer.

??? － Typically referred to as hosted virtualization.

??? － Limits the number of virtual machines you can realistically run.

??? － Example：Microsoft Virtual Server、VMware Server.

??? － 从下图就可以很清楚观察到Type 1 hypervisors和Type 2 hypervisors的差别，

??????? Type 2 hypervisors是执行在操作系统环境中，

??????? 缺点是由实例主机的操作系统管理所有虚拟机器中的运行，

??????? 相对的，运行速度会比较慢，但是很方便，比较没有相容性的问题。

其中Type 1 hypervisors又可根据其搭配的核心的不同，

分为Monolithic hypervisor或Microkernel hypervisors。

What is Monolithic Hypervisor?

??? Monolithic hypervisors design involves using hypervisor-aware device drivers that are hosted within and

??? managed.

??? － Do not need a controlling,or parent,operating system.(benefit)

??? － Device drivers must be specifically developed for the hypervisor.(drawback)

??? － Example：VMware ESX Server.

??? － 从上述可知，Monolithic hypervisor让所有虚拟机器透过hypervisor-aware的驱动程序直接存取与目标硬

??????? 体。

??????? 这样的优点是不需要控制用的操作系统，

??????? 但缺点是此hypervisor-aware的驱动程序是被包含在核心中，

??????? 弹性不足，对于硬件的限制很多，

??????? 必须依据原厂指定的机种或是配备，才能成功地安装与启用。

What is Microkernel Hypervisors?

??? Microkernel hypervisors have an operating system acting as the root,partition.

??? － Do not require hypervisor-aware device drivers.

??? － The parent partition provides the execution environment needed for device drivers to access

??????? the underlying physical hardware of the host computer.

??? － Install device drivers only for physical devices in the operating system running in the parent

??????? partition.

??? － The guest operating systems do not have direct access to the underlying hardware.

??? － The guest operating systems can access physical devices only by communicating with the

??????? parent partition.

??? － Example：Microsoft Hyper-V.

??? － 从上述可知，Microkernel hypervisors和Monolithic hypervisor的差别在于

??????? 不需要hypervisor-aware的驱动程序，

??????? 现有的驱动程序可以立即被使用于虚拟化环境中，

??????? 使得Hypervisor更小、更稳定，耗损也较小。

参考数据：

Understanding Microsoft Virtualization Solutions,by Mitch Tulloch with the Microsoft Virtualization Teams.

原文:大专栏 ?[虚拟] Hypervisor