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Notes on Virtualization
Subject: Cloud Computing

Introduction:
Virtualization is an enabling technology for the different cloud
computing services
...
In this note I going
to discuss about virtualization technology and the benefits of
using this technology
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The capital expenditure (CapEx) and
operational expenditure (OpEx) of buying those resources and
maintaining this large infrastructure is really high, at the same
time Return on investment (ROI) of buying additional
infrastructure are very low
...

Industries adopt virtualization in their organization because of
the following benefits:
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

Better resource utilization
Increase ROI
Dynamic date center
Supports green IT
Eases administration
Improves disaster recovery

While virtualization offers many benefits, it also come with
some drawbacks:
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Single point of failure
Demands high-end and powerful infrastructure
May lead to lower performance
Requires specialized skill set
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These resources are –
memory, processors, storage, and network
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Processor Virtualization:
Processor Virtualization allows the VMs (virtual machines) to
share the virtual processors that are abstracted from the
physical processors available at the underlying infrastructure
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The
virtualization layer will be normally any Hypervisors
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Processor virtualization from a single hardware is shown the
figure below

2
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The main idea of the main
memory virtualization is to map the virtual page number to the
physical page numbers
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Memory virtualization can also be achieved by using the
hypervisor software
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The concept of Memory Virtualization is shown in the
below figure: -

3
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The virtualized storage will
be called a logical storage
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It can be achieved
through the hypervisors
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The other advanced storage virtualization
techniques are storage area networks (SAN) and networkattached storage (NAS)
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Network Virtualization:
Network virtualization is the process of abstracting physical
networking components to form a virtual network
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The virtual
hardware and software resources
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The concept of network virtualization is shows below:

5
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It aggregates the heterogeneous data from the
different sources to a single virtual volume of data
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It is mainly used in
data integration, business intelligence, and cloud computing
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Data Virtualization:

6
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This offers the
ability to the user to use the application without need to install
any software or tools in the machine
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These applications will be developed and hosted in the
central server
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The concept of application virtualization is shown in the figure
below

Different Approaches to Virtualization:
There are three different approaches to virtualization , these
are:
1
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Paravirtualization
3
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Protection rings are used to isolate the
OS from untrusted user applications
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In protection ring architecture,
the rings are arranged in hierarchical order from ring 0 to ring
3 as shown in the Figure below
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Normally, the
highly trusted OS instructions will run in ring 0, and it has
unrestricted access to physical resources
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The other two rings (ring 1 and ring 2) are
allotted for device drivers
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For example, any user
application from ring 3 cannot directly access any physical
resources as it is the least privileged level
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Depending on the type of virtualization, the hypervisor
and guest OS will run in different privilege levels
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Full Hypervisor:
In full virtualization, the guest OS is completely abstracted
from the underlying infrastructure
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The guest OS is not aware
that it is virtualized and thinks it is running on the real
hardware
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The guest OS resides at ring 1 and has the least privilege
than the hypervisor
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It requires the help of
hypervisors to communicate with the underlying infrastructure
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This is shown the figure below:

Pros:
 This approach provides the best isolation and security for
the VMs
...

 The virtual guest OS can be easily migrated to work in
native hardware
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Cons:
 Binary translation is an additional, overhead, and it
reduces the overall system performance
...

Para Virtualization:

This is also known as Partial Virtualization or OS-Assisted
virtualization and provides partial simulation of underlying
infrastructure
...
It replaces the translation of
non-virtualized OS requests with hypercalls
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This direct communication
between the guest OS and hypervisor improves performance
and efficiency
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 It is easier to implement than full virtualization as there is
no need for special hardware
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 The modified guest OS cannot be migrated to run on
physical hardware
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Hardware-Assisted Virtualization:
In this approach hardware vendors like Intel and AMD, offer
the support for virtualization, which eliminates much overhead
involved in the binary translation and guest OS modification
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For Example, Intel releases its Intel Virtualization
Technology (VT-x) and AMD releases AMD-V to simplify the
virtualization techniques
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In hardware-assisted virtualization, the
VMM has the highest privilege (root privilege) level even
though it is working below ring 0
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This is shown in the figure below
:

Pros:
 It reduces the additional overhead of binary translation in
full virtualization
 It
eliminates
the
guest
OS
modification
in
paravirtualization
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All x86/x86_64 processors do not support hardwareassisted virtualization features
...


Let’s summarize all these different Approach to Virtualization:

What is Hypervisor?
Hypervisors are the software tool that sits in between
VMs Physical infrastructure and provides the required
virtual infrastructure for VMs
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The hypervisors are also called VMM (Virtual machine
monitor)
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Types of Hypervisors

Before hypervisors are introduced, there was a one-toone relationship between hardware and OSs
...
After
the hypervisors are introduced, it became a one-tomany relationship
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Hypervisors
are generally classified into two categories:
1
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Type 2 or hosted hypervisors
Type 1 or bare metal hypervisor:
It is also known as bare metal or native hypervisor
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This type of hypervisors are used for servers that
handle heavy load and require more security
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Showing figure of Type 1 or bare meal VMM

Type 2 or hosted hypervisor:

Type 2 hypervisors are also known as embedded or
hosted hypervisors
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These type of hypervisors are installed on
the host OS as a software program
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So, it is
recommended to use type 2 hypervisors only on client
systems where efficiency is less critical
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