Setting up Xen - CASE STUDY
Setting up Xen
Xen Project creates a Virtual Machine Monitor (VMM) also known as a hypervisor, this is a software system that allows the execution of multiple virtual guest operating systems simultaneously on a single physical machine. In particular, the project creates a Type 1 or “bare-metal” hypervisor, meaning that it runs directly on top of the physical machine as opposed to within an operating system. Guest virtual machines running on a Xen Project Hypervisor are known as “domains” and a special domain known as dom0 is responsible for controlling the hypervisor and starting other guest operating systems. These other guest operating systems are called Domus, this is because these domains are “unprivileged” in the sense they cannot control the hypervisor or start/stop other domains. Our hypervisor supports two primary types of virtualization: para-virtualization and hardware virtual machine (HVM) also known as “full virtualization”. Para-virtualization uses modified guest operating systems that we refer to as enlightened guests. These operating systems are aware that they are being virtualized and as such don’t require virtual “hardware” devices, instead they make special calls to the hypervisor that allow them to access CPUs, storage and network resources. In contrast HVM guests need not be modified as the hypervisor will create a fully virtual set of hardware devices for this machine that resemble a physical x86 computer. This emulation requires much more overhead than the paravirtualization approach but allows unmodified guest operating systems like Microsoft Windows to run on top of the hypervisor. HVM support requires special CPU extensions
VT-x for Intel processors and AMD-V for AMD based machines. This technology is now prevalent and all recent servers and desktop systems should be equipped with them. A third type of virtualization though not discussed in this guide is called PVHVM or “Para-virtualisation on HVM” which is a HVM domain with para-virtualized storage, network and other devices. This provides the best of both worlds by reducing expensive emulation but providing hardware accelerated CPU and memory access.
Xen Project creates a Virtual Machine Monitor (VMM) also known as a hypervisor, this is a software system that allows the execution of multiple virtual guest operating systems simultaneously on a single physical machine. In particular, the project creates a Type 1 or “bare-metal” hypervisor, meaning that it runs directly on top of the physical machine as opposed to within an operating system. Guest virtual machines running on a Xen Project Hypervisor are known as “domains” and a special domain known as dom0 is responsible for controlling the hypervisor and starting other guest operating systems. These other guest operating systems are called Domus, this is because these domains are “unprivileged” in the sense they cannot control the hypervisor or start/stop other domains. Our hypervisor supports two primary types of virtualization: para-virtualization and hardware virtual machine (HVM) also known as “full virtualization”. Para-virtualization uses modified guest operating systems that we refer to as enlightened guests. These operating systems are aware that they are being virtualized and as such don’t require virtual “hardware” devices, instead they make special calls to the hypervisor that allow them to access CPUs, storage and network resources. In contrast HVM guests need not be modified as the hypervisor will create a fully virtual set of hardware devices for this machine that resemble a physical x86 computer. This emulation requires much more overhead than the paravirtualization approach but allows unmodified guest operating systems like Microsoft Windows to run on top of the hypervisor. HVM support requires special CPU extensions
VT-x for Intel processors and AMD-V for AMD based machines. This technology is now prevalent and all recent servers and desktop systems should be equipped with them. A third type of virtualization though not discussed in this guide is called PVHVM or “Para-virtualisation on HVM” which is a HVM domain with para-virtualized storage, network and other devices. This provides the best of both worlds by reducing expensive emulation but providing hardware accelerated CPU and memory access.
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