Virtualization
• Virtualization is nothing more than an abstraction over physical
resources to make them shareable by a number of physical users.
• Virtualization allows multiple operating system instances to run
concurrently on a single computer, it is a means of separating
hardware from a single operating system.
A physical server on which one or more virtual
machines are running is defined as host.
The virtual machines are called guests.
A hypervisor or Virtual Machine Monitor
(VMM) is a piece of software, firmware or
hardware that creates and runs virtual
machines.
Virtual Machines
VM technology allows multiple virtual machines to run on a single
physical machine.
App App App App App
Guest OS Guest OS Guest OS VirtualBox
(Linux) (Windows)
(NetBSD)
VM VM VM VMWare
Virtual Machine Monitor (VMM) / Hypervisor
Hardware
Virtualization
Cloud and
• Virtualization
Virtual Workspaces:
– An abstraction of an execution environment that can be made dynamically available to
authorized clients by using well-defined protocols,
– Resource quota (e.g. CPU, memory share),
– Software configuration (e.g. OS).
• Implement on Virtual Machines (VMs):
– Abstraction of a physical host machine,
– Hypervisor intercepts and emulates instructions from VMs, and allows management of VMs,
– VMWare, Xen, KVM etc. App App App
• Provide infrastructure API: OS OS OS
Hypervisor
– Plug-ins to hardware/support
structures Hardware
Virtualized Stack
Need a virtualization software
Only a virtualization software can "imitate" the hardware. It
manages the Virtual Machines, so we normally call it virtual
machine manager.
Open-Source virtualization software
VirtualBox
Commercial virtualization software
VMware workstation –- Paid one
Advantages of virtual machines
– Run operating systems where the physical hardware is unavailable,
– Easier to create new machines, backup machines, etc.,
– Software testing using “clean” installs of operating systems and
software,
– Emulate more machines than are physically available,
– Timeshare lightly loaded systems on one host,
– Debug problems (suspend and resume the problem machine),
– Easy migration of virtual machines (shutdown needed or not).
– Sandbox Does not affect anything on host OS
– Networked
– Resource utilization
– Isolation/interdependence
Virtual Machine Monitor
• The host software that provides virtualization is often referred to
as a virtual machine monitor (VMM) or hypervisor.
• The VMM gives each virtual machine an illusion of a complete
computer to itself.
8
Architecture
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Different types of
Virtualization
Full Virtualization Para-Virtualization OS-level Virtualization
Full Virtualization
The hypervisor interacts directly with the physical server's
CPU and disk space.
The hypervisor keeps each virtual server completely
independent and unaware of the other virtual servers
running on the physical machine.
Each guest server runs on its own OS -- you can even have
one guest running on Linux and another on Windows.
Full Virtualization (Contd..)
As virtual servers run applications, the hypervisor relays resources
from the physical machine to the appropriate virtual server.
Hypervisors have their own processing needs, which means that
the physical server must reserve some processing power and
resources to run the hypervisor application.
This can impact overall server performance and slow down
applications.
Full Virtualization
Full virtualization provides a complete simulation of the underlying
hardware and is a technique used to provide support for unmodified
guest operating systems.
The term unmodified refers to operating system kernels which have not
been altered to run on a hypervisor.
While full virtualization comes with a performance penalty, the
technique permits running unmodified operating system, which is ideal,
particularly when source is unavailable such as with proprietary
operating systems.
Full Virtualization
Para-Virtualization
The fundamental issue with full virtualization is the emulation of
devices within the hypervisor.
A solution to this problem is to make the guest operating system
aware that it's being virtualized.
With this knowledge, the guest OS can short circuit its drivers to
minimize the overhead of communicating with physical devices.
In this way, the guest OS drivers and hypervisor drivers integrate with
one another to efficiently enable and share physical device access.
Low-level emulation of devices is removed, replaced with cooperating
guest and hypervisor drivers.
Para-Virtualization
Para virtualization
• Pros
• Improved Performance
• Cons
• The downside of para-virtualization is that the guest must
be modified to integrate hypervisor awareness
OS-level Virtualization
• An OS-level virtualization approach doesn't use a hypervisor at all.
• Instead, the virtualization capability is part of the host OS, which
performs all the functions of a fully virtualized hypervisor.
• The biggest limitation of this approach is that all the guest servers
must run the same OS.
• Examples: FreeBSD Jails, Solaris Containers.
OS-level Virtualization
OS-level Virtualization
• Shared kernel virtualization or operating system virtualization
takes advantage of the architectural design of Linux and UNIX
based operating systems.
• At the core of the operating system is the kernel.
• The kernel handles all the interactions between the operating
system and the physical hardware.
OS-level Virtualization
The second key component is the root file system which contains all the
libraries, files and utilities necessary for the operating system to function.
Under shared kernel virtualization the virtual guest systems each have
their own root file system but share the kernel of the host operating
system.
OS level virtualization is based on the creation of isolated containers or
partitions on a single physical server, and the use of OS instances for each
guest application environment to work independently of the other
partitions.
Applications of OS-level Virtualization
• It is an ideal approach for web hosting companies which have multiple
virtual web servers running on a single box.
• Another example would be a company that has to manage multiple
SQL databases or any other scenario where many similar or identical
servers need to be hosted or managed within the same datacenter.
Different Types of Hypervisors
• Type 1
• Type 2
Type 1 Hypervisor
• A hypervisor running on bare metal is called Type 1 Hypervisor or native
Hypervisor.
• No host operating system is required, they are installed on bare metal.
• Bare metal hypervisors are faster and more efficient as they do not need
to go through the operating system and other layers that usually make
hosted hypervisors slower.
• Examples
• Vmware ESX
• Citrix XenServer
• Oracle VM Server
Type 2 Hypervisor
• Installed over an operating System and are referred to as Type 2
Hypervisor or hosted Hypervisor.
• Hosted hypervisors are much easier to set up than bare metal
hypervisors because you have an OS to work with.
• These are also compatible with a broad range of hardware.
• Examples
• KVM
• Microsoft Hyper-V (run over Windows Server)
• VirtualBox
• Vmware Workstation
Type 1 Hypervisor vs. Type 2
Hypervisor
According to IBM, Type 1 hypervisors provide higher
performance, availability, and security than Type 2
hypervisors.
Benefits of Virtualization
• Resource Pooling (thus maximum resource utilization)
• Server Consolidation (thus saving energy and cost)
• VM Migration (Refers to moving a server environment from one place
to another)
• Load balancing
• Maintenance
• Failover
• Redundancy
• Isolated machines (Useful for testing operating systems and new
applications)
Load Balancing
• Load Balancing means the ability to spread the load of processing
over a number of separate systems for an overall performance
increase in processing incoming requests.
• It represents the ability to transfer any portion of the processing for a
system request to another independent system that will handle it
concurrently. Eg. Web/Database Server.
