A Guide to Key Virtualization Terminology
One of the most important steps in mastering a new technology is learning the associated terminology or vocabulary. In the Information Technology (IT) field, as much of the terminology is often used inconsistently. The following defines the terminology associated with IT virtualization. .
This section defines many of the most commonly used terms in the virtualization vocabulary.. These are straight forward, commonly accepted definitions.
Virtual Machine (VM) – A set of virtual hardware devices, including virtual CPU, virtual RAM, virtual I/O devices, and other virtual hardware devices. Software that resembles and behaves like a traditional, physical server and runs a traditional operating system (OS).
Virtual Server – A VM running a server OS such as a Windows Server or a Red Hat Enterprise Linux Server. A virtual server typically runs one server-based application.
Virtual Desktop – A VM that is running a desktop OS, such as Windows or Red Hat Enterprise Desktop. A virtual desktop typically has one direct, concurrent user.
Virtual Hardware Device – A software component that resembles and behaves like a specific hardware device. The guest OS and software applications in the VM behave as though the virtual hardware device is actually a physical hardware device. A VM is a set of virtual hardware devices that correspond to the set of devices found in traditional, physical servers, such as virtual CPUs, virtual RAM, virtual storage adapters, and virtual Ethernet adapters.
Virtual CPU) – Software that resembles and behaves ike a traditional, physical CPU. Depending on the underlying technology, vCPUs could be software-emulated or software-modified:
Virtual Network – A network provided by virtual switches. It may be an extension of a traditional network that is built on physical switches and VLANs, or, it may be an isolated network formed strictly from virtual switches.
Virtual Infrastructure – A collection of VMs, virtual networks and storage, and other virtual items that can deploy and run business applications, as an alternative to running applications directly on physical infrastructure. It allows IT personnel to install software applications in
traditional OSs, such as Windows and Linux, without needing to know details of the underlying physical infrastructure. The OSs and applications run in VMs, in virtual networks, and on virtual storage.
Virtual Desktop Infrastructure – A set of virtual desktops running on
virtual infrastructure. VDI often involves detailed optimization at the physical infrastructure, virtual infrastructure desktop OS, and application levels to allow close to native performance. VDI management software automatically brokers and connects users to their virtual desktops. VDI management software also automatically provisions virtual desktop pools from VM templates.
Cloud – A complex system that provides a set of services to consumers, without requiring the consumer to understand any of the underlying complexities of the system. Although this definition is simple, it is a highly accepted definition of the term, even when used to describe non-IT clouds. For example, some people consider electricity, water, and cable television services to be provided by clouds. Clouds provide some IT-based service, often utilizing virtual infrastructure. Businesses can use privately owned clouds, externally owned clouds, or both external and private clouds (hybrid clouds).
Infrastructure as a Service (IaaS) – IaaS provides virtual infrastructure as a service where consumers can easily implement and utilize VMs without needing to understand, manage, or own the underlying physical infrastructure.
Software as a Service (SaaS) – Provides software applications as a
service where consumers can easily use applications without needing to
understand, manage, or own the underlying server operating systems, software applications, databases, or infrastructure. Examples of public SaaS are Google Apps and Salesforce CRM
Platform as a Service (PaaS) – Provides a software development platform
as a service where consumers can easily build applications on a provided platform without any need to understand, manage, or own the underlying infrastructure. It allows developers to easily create applications that are easily portable. Examples of public PaaS are Microsoft Azure and Force.com
Clone – Typically refers to the action of copying one VM or VM template to create a new VM. During a clone operation, the VM files are typically copied, renamed, and modified to customize the new VM.
VM Snapshot – A point-in-time capture of the state of a VM. Snapshots allow the user to revert the VM to a previously captured state. A primary use is to undo changes that were made in a VM but are no longer wanted.
Highly Available (HA) – A system or component that has some automatic protection in case of disruption. The protection may allow a small amount of unplanned downtime, but it will automatically correct the issue within a pre-determined time interval.
VM High Availability (VM HA) – Ensures that a VM is automatically made available, although the host on which it runs fails. VM HA may require an automatic reboot of the VM on another host.
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About the Author John A. Davis has been a VMware Certified Instructor (VCI) and VMware Certified Professional (VCP) since 2004,
