What is Virtualization?
What Is Virtualization?
Virtualization is a broad term in general but when we use it
in the IT world, we use it to say we will virtualize our applications,
networks, servers, storage or even client workstation. Virtualization is a
technology that allows an IT administrator to utilize the same hardware to run
multiple software or operating systems by allocating or dedicating the
underlying physical hardware resources of a computer or server. On the other
side we see that the same hardware can run a single operating system and can be
used for a single host or identity, like a web server that is hosting our
internal finance department web application. But if we use virtualization
technology here, we could install server virtualization software (a hypervisor)
on the same piece of hardware, and we could then run multiple independent
virtual instances of many web servers or any type of operating system or
application instance. These completely different instances that we create on
the physical server are referred to as
guest or virtual machines; they exist virtually and so they are known as virtual machines. Although virtual machines
use the same physical resources among all their other siblings on the same
piece of hardware, virtualization software, which is also referred to as a
hypervisor, ensures that the trusted computing base (TCB) concept is always
enforced and doesn't allow the virtual machine to see what data and
communication it's doing with the physical resources. This means that if there
are two virtual machines running on the same physical hardware, each doesn't
know what the other virtual machine running on it is up to or which data the
other virtual machine is providing or taking from the processor and RAM. When
the administrator creates a virtual machine using a hypervisor, it can dedicate
a chunk of physical RAM and processor cycles to the virtual machine; this
allocation can be either static or dynamic. When we configure static RAM for a
virtual machine, let's say 1,024 MB, the virtual machine is restricted to
always show its virtual RAM as 1 GB. However, on the other side, if we want we
can configure dynamic memory for the virtual machine, so we could set the
startup RAM of 1,024 MB and allow the virtual machine to go up to 10,240 MB. In
the same way, we can configure the virtual machine to have either one logical
processor or four logical processors.
Okay, we discussed virtual RAM and processors for a virtual
machine; what about the hard disk or storage of a virtual machine? Here you go;
just like virtual RAM and processor, we create virtual hard disk (VHD) in the
Hyper-V case. VHD is a file-based storage for a virtual machine. It gets added
or associated to a virtual machine, and then the virtual machine sees this VHD
file associated to a virtual machine instance as its hard disk. The more VHDs
you create and associate to a virtual machine, the more virtual hard disk space
will be assigned to that virtual machine. We could also dedicate a physical
disk to a virtual machine, so if we don't create a file-based virtual hard disk
for a virtual machine, then we can associate a physical hard disk or SAN LUN associated
on the virtualization server to the virtual machine. Virtualization can be set
up in the form of a shared service where we configure the identical type of
virtualization servers (a cluster), and this shared form of virtualization
server allows us to migrate virtual machines from one server to another, in
case one virtualization server goes down or the administrator wants to perform
maintenance on the physical server.
Author: Syed Zahir Hussain Shah
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