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What is Virtualization
Virtualization -- the abstraction of computer resources.Definition : Virtualization is a framework or methodology of dividing the resources of a computer into multiple execution environments, by applying one or more concepts or technologies such as hardware and software partitioning, timesharing, partial or complete machine simulation, emulation, and quality of service.
Virtualization hides the physical characteristics of computing resources from their users, be they applications, or end users.
By virtualizing the machine, we are able to run several operating systems (and all of their applications) at the same time.
Why to Virtualize?
Flexibility: more than one instance
Availability: temporary migration, if physical node is down
Scalability: very easy to insert a physical node with the basic cluster
Hardware utilization: virtual machines utilize hardwareresources that are left idle
Security: Using multiple virtual machines, it is possible toseparate services by running one service on each virtualmachine. This approach is also called jailing of services.
Types of Virtualization
Platform Virtualization (Close to Cloud Computing)i. Full Virtualizationii. Paravirtualizationiii. Hardware-assisted Virtualizationiv. Partial Virtualizationv. OS-level Virtualization
Memory Virtualization
Desktop Virtualization
Application Virtualization
Network (Device and I/O) Virtualization
Key Properties of VMs
Partitioning
-Run multiple operating systems on one physical machine
-Divide system resources between virtual machines
Isolation
-Virtual machines are completely isolated from the host machine and other virtual machines. If a virtual machine crashes, all others are unaffected.
-Data does not leak across virtual machines.
Encapsulation
-Entire state of the virtual machine can be saved to files
-Move and copy virtual machines as easily as moving and copying files
Hardware Independence
-Provision or migrate any virtual machine to any similar or different physical server
VMM/Hypervisor
A hypervisor, also called a virtual machine manager(VMM), is a program that allows multiple operating systems to share a single hardware host.
Each operating system appears to have the host's processor, memory, and other resources all to itself.
Host – underlying hardware system
Guest – process provided with virtual copy of the host (Usually an operating system).
Advantages of Virtualization
Zero downtime maintenance.
Freedom from vendor-imposed upgrade cycles.
Instant provisioning.
Pooling hardware resource.
Virtual hardware supports legacy operating systems efficiently.
Dynamic resource sharing.
Security and fault isolation.
Business continuity, backups, and automated restoration.