VIRTUALIZATION BASICS

Virtualization is the creation of a virtual (rather than actual) version of something, such as an operating system, a server, a storage device or network resources.

You probably know a little about virtualization if you have ever divided your hard drive into different partitions. A partition is the logical division of a hard disk drive to create, in effect, two separate hard drives.

Operating system virtualization is the use of software to allow a piece of hardware to run multiple operating system images at the same time. The technology got its start on mainframes decades ago, allowing administrators to avoid wasting expensive processing power.

In 2005, virtualization software was adopted faster than anyone imagined, including the experts. There are three areas of IT where virtualization is making headroads, network virtualization, storage virtualization and server virtualization:

TYPES

• Network virtualization is a method of combining the available resources in a network by splitting up the available bandwidth into channels, each of which is independent from the others, and each of which can be assigned (or reassigned) to a particular server or device in real time. The idea is that virtualization disguises the true complexity of the network by separating it into manageable parts, much like your partitioned hard drive makes it easier to manage your files.
• Storage virtualization is the pooling of physical storage from multiple network storage devices into what appears to be a single storage device that is managed from a central console. Storage virtualization is commonly used in storage area networks (SANs).
• Server virtualization is the masking of server resources (including the number and identity of individual physical servers, processors, and operating systems) from server users. The intention is to spare the user from having to understand and manage complicated details of server resources while increasing resource sharing and utilization and maintaining the capacity to expand later.

• · Platform virtualization, which separates an operating system from the underlying platform resources
• Full virtualization, sensitive instructions replaced by binary translation or trapped by hardware - all software can run in the VM, e.g. IBM's CP/CMS, VirtualBox, VMware Workstation
• Hardware-assisted virtualization, CPU traps sensitive instructions - runs unmodified guest OS; used e.g. by VMware Workstation, Xen, KVM
• Partial virtualization, for specific applications rather than the operating system
• Paravirtualization, a virtualization technique that presents a software interface to virtual machines that is similar, but not identical, to that of the underlying hardware, thereby requiring guest operating systems to be adapted, e.g. Xen in early stage
• Operating system-level virtualization, a method where the operating system allows for multiple user-space instances (virtual hosting, chroot jail + resource management)
• Application virtualization, the hosting of individual applications on alien hardware/software
• Portable application, a computer software program that runs from a removable storage device as a USB flash drive
• Cross-platform virtualization, allows software compiled for a specific CPU and operating system to run unmodified on different CPUs and/or operating systems
• Virtual appliance, a virtual machine image designed to run on a virtualization platform
• Emulation or simulation

· Virtual memory, which allows uniform, contiguous addressing of physically separate and non-contiguous memory and disk areas

· Storage virtualization, the process of completely abstracting logical storage from physical storage

· Memory virtualization, aggregates RAM resources from networked systems into virtualized memory pool

· Network virtualization, creation of a virtualised network addressing space within or across network subnets

• Virtual private network (VPN), a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network(s), such as the Internet

· Desktop virtualization, the remote manipulation of a computer desktop

· Database virtualization, the decoupling of the database layer, which lies between the storage and application layers within the application stack

· Timeline of virtualization development, further work in this area

· Virtual Chargeback, the allocation