"imperfect virtualization can and often is preferable to perfect virtualization"
Linux virtualization can be used for isolating specific apps, programming code or even an operating system itself, as well as for security and performance testing purposes.
The evolution of virtualization greatly revolves around this piece of very important software termed as hypervisor.
Hypervisor: A software layer or subsystem that controls hardware and provides guest operating systems with access to underlying hardware. The hypervisor allows multiple operating systems, called guests, to run on the same physical system by offering virtualized hardware to the guest operating system
Bare-metal Hypervisor. This type of hypervisor (pictured at the beginning of the article) is deployed as a bare-metal installation. This means that the first thing to be installed on a server as the operating system will be the hypervisor. The benefit of this software is that the hypervisor will communicate directly with the underlying physical server hardware. Those resources are then paravirtualized and delivered to the running VMs. This is the preferred method for many production systems.
Hosted Hypervisor. This model (shown below) is also known as a hosted hypervisor. The software is not installed onto the bare-metal, but instead is loaded on top of an already live operating system. For example, a server running Windows Server 2008R2 can have VMware Workstation 8 installed on top of that OS. Although there is an extra hop for the resources to take when they pass through to the VM – the latency is minimal and with today’s modern software enhancements, the hypervisor can still perform optimally.
Important terms to understand virtualization.
Full virtualization: The guest operating system and any applications on the guest virtual machine are unaware of their virtualized environment and run normally. Hardware-assisted virtualization is the technique used for full virtualization with KVM (Kernel-based Virtual Machine) in Red Hat Enterprise Linux.
Para-virtualization: After the guest VM is installed on top of the hypervisor, there usually is a set of tools which are installed into the guest VM. These tools provide a set of operations and drivers for the guest VM to run more optimally. For example, although natively installed drivers for a NIC will work, paravirtualized NIC drivers will communicate with the underlying physical layer much more efficiently. Furthermore, advanced networking configurations become a reality when paravirtualized NIC drivers are deployed.
Software virtualization (or emulation): Software virtualization uses slower binary translation and other emulation techniques to run unmodified operating systems.
Migration: Migration describes the process of moving a guest virtual machine from one host to another. This is possible because the virtual machines are running in a virtualized environment instead of directly on the hardware. There are two ways to migrate a virtual machine: live and offline.
eg. Load balancing, Upgrading or making changes to the host, Energy saving, Geographic migration
Key : KVM, VMware ESX, and Hyper-V.
Linux virtualization can be used for isolating specific apps, programming code or even an operating system itself, as well as for security and performance testing purposes.
The evolution of virtualization greatly revolves around this piece of very important software termed as hypervisor.
Hypervisor: A software layer or subsystem that controls hardware and provides guest operating systems with access to underlying hardware. The hypervisor allows multiple operating systems, called guests, to run on the same physical system by offering virtualized hardware to the guest operating system
Bare-metal Hypervisor. This type of hypervisor (pictured at the beginning of the article) is deployed as a bare-metal installation. This means that the first thing to be installed on a server as the operating system will be the hypervisor. The benefit of this software is that the hypervisor will communicate directly with the underlying physical server hardware. Those resources are then paravirtualized and delivered to the running VMs. This is the preferred method for many production systems.
Hosted Hypervisor. This model (shown below) is also known as a hosted hypervisor. The software is not installed onto the bare-metal, but instead is loaded on top of an already live operating system. For example, a server running Windows Server 2008R2 can have VMware Workstation 8 installed on top of that OS. Although there is an extra hop for the resources to take when they pass through to the VM – the latency is minimal and with today’s modern software enhancements, the hypervisor can still perform optimally.
Important terms to understand virtualization.
Full virtualization: The guest operating system and any applications on the guest virtual machine are unaware of their virtualized environment and run normally. Hardware-assisted virtualization is the technique used for full virtualization with KVM (Kernel-based Virtual Machine) in Red Hat Enterprise Linux.
Para-virtualization: After the guest VM is installed on top of the hypervisor, there usually is a set of tools which are installed into the guest VM. These tools provide a set of operations and drivers for the guest VM to run more optimally. For example, although natively installed drivers for a NIC will work, paravirtualized NIC drivers will communicate with the underlying physical layer much more efficiently. Furthermore, advanced networking configurations become a reality when paravirtualized NIC drivers are deployed.
Software virtualization (or emulation): Software virtualization uses slower binary translation and other emulation techniques to run unmodified operating systems.
Migration: Migration describes the process of moving a guest virtual machine from one host to another. This is possible because the virtual machines are running in a virtualized environment instead of directly on the hardware. There are two ways to migrate a virtual machine: live and offline.
eg. Load balancing, Upgrading or making changes to the host, Energy saving, Geographic migration
Key : KVM, VMware ESX, and Hyper-V.
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