2 How Virtualization Works

Question 1

What is a Hypervisor?

Answer 1

A hypervisor is a software program that separates a computer’s software from its hardware and makes virtualization possible.

Question 2

What Are the Benefits of Hypervisors?

Answer 2

• Capital expenses are reduced.
• Operating expenses are reduced.
• Each OS shares the resources on the server.
• One physical server can host multiple guest operating systems.

Question 3

Do Hypervisors Require an OS?

Answer 3

It depends on the type of hypervisor.

Question 4

What is Bare-Metal Hypervisor?

Answer 4

• Also called a type 1 hypervisor, a bare-metal hypervisor is installed directly on the server hardware.
• You do not need to install an OS before installing the bare-metal hypervisor.
• It is easier to maintain than a hosted hypervisor.
• Example: VMware ESXi.

Question 5

What is Hosted Hypervisors?

Answer 5

• Also called a type 2 hypervisor, a hosted hypervisor is installed on an OS.
• You install the hosted hypervisor on an OS in the same way that you install an application.
• Example: VMware Workstation and VMware Fusion.

Question 6

How Transforming Physical Resources into Virtual Resources?

Answer 6

1. • When the hypervisor starts, it takes control of the physical resources of the host.
2. • You create VMs on the ESXi host:
     - When creating a physical server, you assemble the required physical CPU, RAM, and other resources. Similarly, for VMs, you specify the software equivalent of the hardware resources that you need to run the guest OS.
3. • The hypervisor creates virtual hardware that VMs can use:
     - The hypervisor abstracts the processor, memory, disk, network, and other resources and creates a virtual version of these resources, which are called virtual hardware.
4. • The hypervisor manages the virtual hardware assigned to the VMs that it runs.
5. • You install a guest OS inside the VM in the same way that you install an OS on a physical computer.

Question 7

Virtual CPU

Answer 7

The ESXi host manages how much compute access is available for each VM:

• When a guest OS requests CPU for an application, ESXi finds the available resource and makes it visible to the VM.
• Multiple VMs might demand CPU from the ESXi host simultaneously.
• If the requested CPU is more than the available CPU on the host, ESXi schedules the VMs to take turns (share) using the CPU.

Question 8

Virtual Memory

Answer 8

• The sum of configured memory sizes of all VMs might exceed the amount of available physical memory on the host. For example, an ESXi host with 8 GB RAM can run three VMs of total allocated memory of 11 GB.
• The memory resource settings for a VM determine how much of the host’s memory is allocated to the VM.
• The virtual memory size determines how much memory is available to applications that run in the VM.
• VMs do not always use 100% of the allocated memory.

Question 9

Virtual Networking

Answer 9

VMs can share access to the same virtual switch and the same physical network interface cards (NICs) on the host:
- Share the same virtual switch to communicate with other VMs on the host.
- Share the same physical NIC to communicate with other devices outside the ESXi host.
For example, if your ESXi host has only one physical NIC, you can use one virtual switch to direct the network traffic of multiple VMs through that NIC.

Question 10

Virtual Disks

Answer 10

Multiple ESXi hosts can read or write to shared storage concurrently.

For example, ESXi hosts connect to a large array of disks in a server room through a network:

• The ESXi hosts recognize those devices as storage space that they can present to VMs as virtual disks.
• VMs can store application data and their VM files in these virtual disks.
• A VM with a virtual disk that is stored on shared storage can be powered on by using any ESXi host that has access to that storage.

Question 11

Virtual GPUs

Answer 11

• Using virtualization, VMs can share specialized hardware devices or devices that are difficult or expensive to obtain.

For example, an ESXi host is dedicated to development and testing:

• The host has four GPUs.
• The total number of allocated GPUs is five.

In this case, you can decide whether to dedicate a full GPU device to one VM, or allow partial sharing of a GPU device by more than one VM, if the GPU supports it.

Question 12

Which statements accurately describe bare-metal hypervisors?

Answer 12

• An example of a bare-metal hypervisor is VMware ESXi.

- Bare-metal hypervisors are installed directly on the computer hardware.

Question 13

After you install a hypervisor, it helps you to virtualize physical resources for VMs. This virtualization of resources follows a sequence of steps.

Answer 13

1. • The hypervisor takes control of the physical resources of the host.
2. • You create a VM and specify the required hardware to run a specific OS.
3. • The hypervisor abstracts the physical resources into virtual hardware.
4. • The hypervisor manages the virtual hardware that is assigned to VMs.
5. • You install a guest operating system inside the VM, just as you do on a physical computer.

Question 14

Which statements accurately describe physical resource sharing?

Answer 14

• The ESXi host can route the network traffic of multiple VMs through the same physical network card.
• You can create 10 VMs with two virtual CPUs each, even though the ESXi host has only four CPUs in total.
• VMs can share the virtual resources that their ESXi host manages.