The document discusses virtualization, explaining the distinction between hardware and software virtualization, including their respective implementations and technologies. It emphasizes the management of virtualization environments, particularly in the context of data centers, highlighting the evolution of management tools to handle increasing complexity through concepts like resource pools and role-based access control. The document also mentions various data center virtualization management solutions, including VMware vCenter and others.

1. VIRTUALIZATION
Virtualization refers to the practice of simulating multiple virtual machines on a single
physical computer.
 Logically each virtual machine has its own virtualized
CPU,
memory,
storage,
networking.
 Through virtualization the underlying hardware resource can be utilized with
more efficiency, applications can run on the same physical computer but its own
runtime environment that is isolated from each other
Different levels of virtualization:
hardware virtualization
software virtualization.
 Hardware virtualization:
 Hardware virtualization means providing a virtual computer by simulating the
underlying hardware, and the virtual computer is capable of running a full copy
of operating system.
Implementations of Hardware virtualization:
Full virtualization: Simulating a full set of the underlying hardware such
that most operating systems could run on top of the virtual machine without modifications
Partial virtualization: Simulating only some key hardware components,
operating systems might need modifications to run in such an environment
Paravirtualization: Does not simulating the underlying hardware, but
rather shares the underlying hardware through virtual machine manager applications, and
most operating systems need modifications to run in such an environment.
 Virtualization on software level usually refers to the practice of providing multiple
isolated runtime environment on top of a single operating system instance, and it is
often called container technology.
 With hardware virtualization, most modern virtualization technologies such as
VMWare, Xen and KVM are a combination of full virtualization and
paravirtualization.
 Virtual machines provided by hardware virtualization technologies usually run a full
copy of operating system, therefore these exist large amount of similar processes
and memory pages on the same host machine.
 Therefore hardware virtualization is usually referred to as heavy-weight virtualization,
and the number of virtual machines that could run on a single host machine is
relatively limited.

2. Architecture of virtualization
 software virtualization
 The overhead of running multiple operating system instances does not exist.
 software virtualization is usually referred to as light-weight virtualization, and
the number of virtual runtime environments that could present on a single host
machine is relatively large.
 LXC on Linux can easily provide a large amount of virtualized runtime
environments.
In terms of virtualization technologies, most companies in China seem to focus more on
hardware virtualization, and deploy hardware virtualization in development and production
environments.
For a specific application scenario, the decision between hardware virtualization and
software virtualization should rely on whether the end users needs control over the operating
system.
If the end user only needs control over runtime environment, software virtualization
might be a better choice.

3. Virtualization Management:
In the early days,virtualization
isolated runtime environments on a single physical computer. When the number of physical
computers is small, system administrators can manually login to different servers to carry out
the virtual machine life cycle management tasks.
When the number of physical computers becomes big, some kind of scripting /
application is needed to increase the degree of automation and relief system administrators
from tedious works.
Applications that enables system administrators manage multiple physical and virtual
computers from a single location are called virtualization management tools.
Such tools can usually accomplish the following tasks:
 Manage the life cycles of multiple virtu
 Query and monitor all physical and virtual computers.
 Establish a mapping between the name of virtual machines and the actual virtual
machine instances on different computers such that virtual machine identificat
management becomes easier.
Virtualization Management:
In the early days,virtualization technologies solved the problem of providing multiple
isolated runtime environments on a single physical computer. When the number of physical
computers is small, system administrators can manually login to different servers to carry out
ne life cycle management tasks.
When the number of physical computers becomes big, some kind of scripting /
application is needed to increase the degree of automation and relief system administrators
that enables system administrators manage multiple physical and virtual
computers from a single location are called virtualization management tools.
Such tools can usually accomplish the following tasks:
Manage the life cycles of multiple virtual machines on multiple physical computers.
Query and monitor all physical and virtual computers.
Establish a mapping between the name of virtual machines and the actual virtual
machine instances on different computers such that virtual machine identificat
management becomes easier.
technologies solved the problem of providing multiple
isolated runtime environments on a single physical computer. When the number of physical
computers is small, system administrators can manually login to different servers to carry out
When the number of physical computers becomes big, some kind of scripting /
application is needed to increase the degree of automation and relief system administrators
that enables system administrators manage multiple physical and virtual
computers from a single location are called virtualization management tools.
al machines on multiple physical computers.
Establish a mapping between the name of virtual machines and the actual virtual
machine instances on different computers such that virtual machine identification and

4. Data Center Virtualization:
 In a data center, system administrators need to look after a large amount of different
hardware and applications. As compared to a small cluster, the complexity of a data
center is significantly different.
 Now a simple virtualization management tools is no longer capable of satisfying the
need of system administrators.
 Therefore people developed data center virtualization management software to meet
these new challenges. On the hardware layer, data center virtualization management
software created the concept of “resource pools” to reorganize hardware resources,
where a pool is usually a group of servers with similar configuration and purpose.
 Computing resources are now exposed to the end user in the form of virtual
infrastructure, rather than separate servers.
 On the software layer, data center virtualization software created different roles for
system administrators and regular end users, or more fine-grained role based access
control (RBAC) based on the need of a specific application scenario. System
administrators have the right to manage all the physical servers and virtual machines,
but usually do not interfere the virtual machines that are running normally.
 Regular end users can only carry out virtual machine life cycle management tasks
within the resource pool that are assigned to them, and do not have the right to
manage the physical servers. In the extreme case, regular end users can only see the
resource pool that are assigned to them, without any knowledge of the details about
the resource pool.
Before data center virtualization technology, the action of creating and managing virtual
machines are usually carried out by system administrators. In a data center virtualization
software, based on RBAC the virtual machine life cycle management rights are delegated to
so called “regular users”, therefore relieves the pressure on system administrators.

5. However, for security considerations not all employees in a company can have such a
“regular user” account, which is usually assigned to managers or team leads. It is safe to
assume that in data center virtualization the life cycle of virtual machines are still managed
centrally.
Data center virtualization management software is a further extension of virtualization
management tools. It solved the problem of system complexity which is introduced by the
increasing number of hardware devices and applications.
When specific physical hardware are presented in the form of an abstracted “resource
pool”, managers only need to worry about the size, work load, and health status of various
resource pools, while end users only need to know about the status of the resource pool that is
assigned to them.
Only system administrators need to know by heart the configuration, work load and
status of each and every single physical server. However, with the concept of resource pools,
all physical devices can be reorganized in a relatively logical way, which makes the life of
system administrators easier.
Modern data center virtualization management software usually provides a lot of IT
ops automation functionalities. Such functionalities include:
 Fast deployment of a number of same or similar runtime environments based on
virtual machine templates.
 Monitoring, reporting, notification, and accounting.
 High availability, dynamic workload management, backup and recovery.
Some data center virtualization management software even provides open API’s that
allow system administrators to develop and integrate additional functionalities based on
the actualy application scenarios.
Among the VMWare product family VMWare vCenter is a powerful data center
virtualization management software.
 Other good data center virtualization management softwares include:
Convirt,
XenServer,
Oracle VM and,
OpenQRM.