Big Data Analytics
UNIT-2
Lecture-5
Virtualization
It is the creation of virtual (version of something, such as server, a desktop, a
storage device, an operating system or network resources i.e., resources are made
available to the users but virtually not physically.
It is a technique which allows sharing a single physical instance of resources to
multiple users.
Need of Virtualization:
1. Enhanced Performance (by providing additional resources to user).
2. Limited use of Resources (for better utilization of resources)
3. Shortage of space (lack of resources from user side)
4. Eco-friendly Initiatives (reduces power consumption)
5. Administrative costs (reduces urgent cost from client side)
Advantages of Virtualization:
Economical (Don’t need to buy high-capacity hardware and other resources)
Flexible Operations (you can access it from anywhere and customization can be
done)
Security (provided by cloud service provider)
Eliminated the risk of system failure.
Flexible transfer of data
Faster provisioning of applications and resources.
Greater business continuity and disaster recovery.
Simplified data centre management.
Virtualization Reference Model:
Guest layer
Applica on 1 Applica on 2 Applica on 3
Virtual Images
Virtualization layer
Hyper vision (VMM)
Virtual H/W Virtual Storage Virtual
networking
Host layer
Physical H/W Physical Storage
Physical Networking
Four major components of virtualization reference model are available here.
1. Host Layer:
The host layer represents the original environment where the guest is
supposed to be managed.
All the physical resources and physical networking is present in this layer.
Each guest runs on the host machine using shared resources donated to it
by the host.
The OS works as the host and manages the physical resources
management and the device support.
2. Guest Layer:
The guest represents the system components that interacts with the
virtualization layer rather than with the host.
Guest usually consists of one or more virtual disk files and a VM
definition file.
Virtually machines are centrally managed by a host application that sees
and manages each virtual machine as a different application.
3. Virtualization Layer:
The Virtualization layer is responsible for recreating the same or a
different environment where the guest will operate.
It is an additional abstraction layer between a network and a storage
hardware, computing and the application running on it.
4. Hypervisor
A Hypervisor, also known as virtual machine, monitor (VMM), is a
software that creates and runs virtual machines (VMs)
A Hypervisor allows one host computer to support multiple guest VM’s by
virtually sharing it, resources such as memory and processing.
Implementation Levels of Virtualization:
Application Level
Library (user-API) Level
Operating System Level
Hardware Abstraction layer (HAL) Level
Instruction Set Architecture (ISA) Level
1. Instruction Set Architecture (ISA) Level
In ISA Level implementation, every machine has an instruction set which
is an interface between software and hardware.
An emulator is created which receives all the instructions from the virtual
machines.
The emulator interprets what type of instruction it is and then map that
instruction to the host machines instruction and then that instruction will
be carried out on host machine and the results will be passed to the
emulator and emulator will return it to the virtual machine.
Problems in ISA Level Implementation:
Since every instruction has to be interpreted before mapping it, too
much time is consumed and performance becomes poor.
2. Hardware Abstraction layer (HAL) Level
To overcome the problems of ISA level implementation of virtualization,
we have virtualization at HAL level.
In HAL level, we map the virtual resources with physical resources.
We don’t interpret every instruction (as of in ISA level), but we just check
whether it is privileged or non-privileged (ex. Memory management,
scheduling etc)
If the instruction is not privileged, we simply allow normal execution
become already virtual and physical resources are mapped.
If the instruction is privileged, we pass the control to VMM and it deals
with it accordingly.
Problems in HAL Implementation:
Even after many advancements still there are certain exceptions
which cannot be caught by this method.
Since, in this method each VM is built from scratch i.e., by
installing OS, application suites, networking system etc., so if it is
required to initialize more virtual machine at a single time, then it
will take two much of time.
3. Operating System Level
To overcome the problems of HAL level implementation we can use OS
level virtualization.
In this method each VM is not built from scratch rather we share operating
system between virtual machine along with the H/W.
We keep the base OS same and install only the difference in each single
virtual machine.
Problems with Operating System Level:
The major problem with this is that we can install only those OS in
VMs whose base OS formally is same like for example we can’t
install Ubuntu on a VM whose base OS is windows.
4. Library (user-API) Level
In this type, we use library level interfaces to provide a different virtual
environment (VE) for that application.
In short, we provide user with an emulator with which user can run
application of different OS’s.
5. Application Level:
In this kind of virtualization virtual machine run as an application on the
host operating system.
We create a virtualization layer which is present above the host OS and
encapsulates all the application from the underlying OS.
While all the application are loaded, Host OS provides them with a
runtime environment.
But Virtualization layer replaces a part of this runtime environment and
gives virtual environment to the virtualised application.
