For some of the software packages commonly used to provide platform virtualization, see comparison of platform virtual machines Cloud server A VPS which is dynamic (that is, it can be changed at runtime) is often referred to as a cloud server.
Key attributes for this are: • Additional hardware resources can be added at runtime (CPU, RAM) • Server can be moved to other hardware while the server is running (automatically according to load in some cases) See Cloud computing for more information.
Capacity management 3 Capacity management Capacity Management is a process used to manage information technology (IT).
Its primary goal is to ensure that IT capacity meets current and future business requirements in a cost-effective manner.
One common interpretation of Capacity Management is described in the ITIL framework. ITIL version 3 views capacity management as comprising three sub-processes: business capacity management, service capacity management, and component capacity management (known as resource capacity management in ITIL version 2).
As the usage of IT Services change and functionality evolves, the amount of processing power, memory etc also changes.
If it is possible to understand the demands being made currently, and how they will change over time, this approach proposes that planning for IT Service growth becomes easier and less reactive.
If there are spikes in, for example, processing power at a particular time of the day, it proposes analyzing what is happening at that time and make changes to maximize the existing infrastructure, for example, tune the application, or move a batch cycle to a quieter period.
These activities are intended to optimize performance and efficiency, and to plan for and justify financial investments.
Capacity management is concerned with: • • • • • • Monitoring the performance and throughput or load on a server, server farm, or property Performance analysis of measurement data, including analysis of the impact of new releases on capacity Performance tuning of activities to ensure the most efficient use of existing infrastructure Understanding the demands on the Service and future plans for workload growth (or shrinkage) Influences on demand for computing resources Capacity planning – developing a plan for the Service Capacity management interacts with the discipline of Performance Engineering, both during the requirements and design activities of building a system, and when using performance monitoring as an input for managing capacity of deployed systems.
References  ITIL Capacity Management (http:/ / www.
php?page=Capacity_Management) – The ITIL Open Guide Hardware virtualization 4 Hardware virtualization In computing, hardware virtualization is a virtualization of computers or operating systems.
It hides the physical characteristics of a computing platform from users, instead showing another abstract computing platform.  The software that controls the virtualization used to be called a “control program” at its origins, but nowadays the terms hypervisor or virtual machine monitor are preferred.
Concept The term “virtualization” was coined in the 1960s, to refer to a virtual machine (sometimes called pseudo machine), a term which itself dates from the experimental IBM M44/44X system.
The creation and management of virtual machines has been called platform virtualization, or server virtualization, more recently.
Platform virtualization is performed on a given hardware platform by host software (a control program), which creates a simulated computer environment, a virtual machine, for its guest software.
The guest software is not limited to user applications; many hosts allow the execution of complete operating systems.
The guest software executes as if it were running directly on the physical hardware, with several notable caveats.
Access to physical system resources (such as the network access, display, keyboard, and disk storage) is generally managed at a more restrictive level than the host processor and system-memory.
Guests are often restricted from accessing specific peripheral devices, or may be limited to a subset of the device’s native capabilities, depending on the hardware access policy implemented by the virtualization host.
Virtualization often exacts performance penalties, both in resources required to run the hypervisor, and as well as in reduced performance on the virtual machine compared to running native on the physical machine.
Reasons for virtualization – In case of server consolidation, many small physical servers are replaced by one larger physical server, to increase the utilization of costly hardware resources such as CPU.
Although hardware is consolidated, typically OSs are not.
Instead, each OS running on a physical server becomes converted to a distinct OS running inside a virtual machine.
The large server can “host” many such “guest” virtual machines.
This is known as Physical-to-Virtual (P2V) transformation.
– A virtual machine can be more easily controlled and inspected from outside than a physical one, and its configuration is more flexible.
This is very useful in kernel development and for teaching operating system courses. – A new virtual machine can be provisioned as needed without the need for an up-front hardware purchase.
– A virtual machine can easily be relocated from one physical machine to another as needed.
For example, a salesperson going to a customer can copy a virtual machine with the demonstration software to his laptop, without the need to transport the physical computer.
Likewise, an error inside a virtual machine does not harm the host system, so there is no risk of breaking down the OS on the laptop.
– Because of the easy relocation, virtual machines can be used in disaster recovery scenarios.
However, when multiple VMs are concurrently running on the same physical host, each VM may exhibit a varying and unstable performance, which highly depends on the workload imposed on the system by other VMs, unless proper techniques are used for temporal isolation among virtual machines.
There are several approaches to platform virtualization.
Examples of virtualization scenarios: Running one or more applications that are not supported by the host OS Hardware virtualization A virtual machine running the required guest OS could allow the desired applications to be run, without altering the host OS.
Evaluating an alternate operating system The new OS could be run within a VM, without altering the host OS.
Server virtualization Multiple virtual servers could be run on a single physical server, in order to more fully utilize the hardware resources of the physical server.
Duplicating specific environments A virtual machine could, depending on the virtualization software used, be duplicated and installed on multiple hosts, or restored to a previously backed-up system state.
Creating a protected environment If a guest OS running on a VM becomes infected with malware, the host operating system’s exposure to the risk may be limited, depending on the configuration of the virtualization software.
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