Virtualization Interview Questions and Answers

> What is Virtualization ?
Virtualization is the creation of a virtual (rather than actual) version of something, such as an operating system, a server, a storage device or network resources.

You probably know a little about virtualization if you have ever divided your hard drive into different partitions. A partition is the logical division of a hard disk drive to create, in effect, two separate hard drives.

Operating system virtualization is the use of software to allow a piece of hardware to run multiple operating system images at the same time. The technology got its start on mainframes decades ago, allowing administrators to avoid wasting expensive processing power.

In 2005, virtualization software was adopted faster than anyone imagined, including the experts. There are three areas of IT where virtualization is making headroads, network virtualization, storage virtualization and server virtualization.

>What are the benefits of virtualization ?
There are some well accepted and inherit benefits to using Virtualization. Here are some of them:

*Reduce the number of physical servers
*Reduce the infrastructure needed for your data center (power, cooling, battery backup, network switch ports, KVM ports and space)
*Reduce administrative overhead because servers can be administered from a single console
*Ability to bring up new servers quickly (it could take days or weeks to put in a new physical server but it could take just a few minutes to create a new virtual server from a template)
*Hardware Independence of virtual servers – a virtual server can run on any host server, regardless of the host hardware
*Because of hardware independence, you receive reduce your disaster recovery cost, complexity, and recovery time
*A “greener” datacenter & server environment due to the consolidation
Overall, lower TCO of servers

>What is a Hypervisor ?
You can think of a Hypervisor as the kernel or the core of a virtualization platform. The Hypervisor is also called the Virtual Machine Monitor. The Hypervisor has access to the physical host hardware.

Of the total amount of disk space taken for a virtualization platform (like Hyper-V or VMware ESX), the Hypervisor is, by far, the smallest part. A Type 1 Hypervisor runs on the bare metal of the hardware. Examples of a Type 1 Hypervisor are Hyper-V and ESX Server. A Type 2 Hypervisor is hosted by an operating system. Examples of a Type 2 Hypervisor are VMware Server and Microsoft Virtual Server.

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>What is ESX Server ?
ESX Server is VMware’s flagship enterprise server virtualization platform. It comes in two versions – ESX Server and ESXi Server where the latter has no service console and is the thinnest version available. ESX Server has many optional features like VMotion and VMHA (both discussed below) and some built-in features like the VMFS file system. Most end users purchase VMware ESX Server with some set of optional features in a package called VMware Infrastructure. ESX Server is managed by the VMware Infrastructure Client. Its centralized management platform is called Virtual Center.

>What is Hyper-V ?
Codenamed "Viridian" but given the the formal name of Hyper-V, it is a hypervisor-based Windows Server virtualization platform that is included as a role of Windows Server 2008. Hyper-V enables you to consolidate workloads onto a single physical server using a broad range of services ranging from resource-intensive services like Microsoft SQL Server to third-party applications that may run on previous versions of Windows or Linux.

>What are a host, guest, and virtual machine ?

A host system (host operating system) would be the primary & first installed operating system.  If you are using a bare metal Virtualization platform like Hyper-V or ESX, there really isn’t a host operating system besides the Hypervisor. If you are using a Type-2 Hypervisor like VMware Server or Virtual Server, the host operating system is whatever operating system those applications are installed into.

A guest system (guest operating system) is a virtual guest or virtual machine (VM) that is installed under the host operating system. The guests are the VMs that you run in your virtualization platform.

Some admins also call the host & guest the parent and child.

>What products are available for Server Virtualization ?
Bare Metal Hypervisor / Native / Type 1:

VMware ESX Server
Microsoft Hyper-V
Citrix/Xen Server

Hosted in an OS / Type 2:

VMware Server
Microsoft Virtual Server
Parallels Server

> What products are available for desktop virtualization ?
Host in an OS / Type 2 / intended for workstations:

VMware Workstation
Microsoft Virtual PC
Parallels Workstation
VMware Fusion for Mac OS
Parallels Desktop for Mac OS

>What is the difference between ESX Server and VMware Server ?
While both ESX Server and VMware Server are server virtualization products, the difference is that VMware ESX installs and runs on the bare metal of a physical server where as VMware Server needs a base operating system. In other words, VMware ESX has a type 1 hypervisor where as VMware Server has a type 2 hypervisor.

You will obtain must better performance from ESX Server as it has much less overhead. ESX Server also has many features available such as VMFS, VMotion, VMHA, and DRS. On the other hand, ESX Server is also a commercial product that must be purchased where as VMware Server is a free product. VMware Server is an excellent option to choose to slowly migrate to server consolidation at a low cost. VMware Server is also an excellent way to learn about virtualization as well as a way to run multiple operating systems on your desktop PC, at no cost.

>What is the difference between Hyper-V and Virtual Server ?
Like the difference between ESX Server and VMware Server, Hyper-V and Virtual server have similar differences. Hyper-V is a type-1 hypervisor where Virtual Server is a type 2 hypervisor. Virtual Server requires that you first host a Windows operating system to load it.

Hyper-V is meant to be a higher performance commercial virtualization platform with a centralized management platform and 3rd party add-ons. Virtual Server, on the other hand, is a free virtualization platform meant for the desktop or for small-scale server virtualization solutions.

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>What is the difference between emulation, native virtualization, and paravirtualization ?
Emulation is where software is used to simulate hardware for a guest operating system to run in. This has been used in the past but is difficult to do and offers low performance.

Native virtualization (or full virtualization) is where a type-2 hypervisor is used to partially allow access to the hardware and partially to simulate hardware in order to allow you to load a full operating system. This is used by emulation packages like VMware Server, Workstation, Virtual PC, and Virtual Server.

Paravirtualization is where the guest operating systems run on the hypervisor, allowing for higher performance and efficiency. For more technical information and videos on this topic, visit VMware’s Technology Preview for Transparent Virtualization. Examples of paravirtualization are Microsoft Hyper-V and VMware ESX Server.

>What are the different types of virtualization ?
Server Virtualization – consolidating multiple physical servers into virtual servers that run on a single physical server.
Application Virtualization – an application runs on another host from where it is installed in a variety of ways. It could be done by application streaming, desktop virtualization or VDI, or a VM package (like VMware ACE creates with a player). Microsoft Softgrid is an example of Application virtualization.
Presentation Virtualization – This is what Citrix Met frame (and the ICA protocol) as well as Microsoft Terminal Services (and RDP) are able to create. With presentation virtualization, an application actually runs on another host and all that you see on the client is the screen from where it is run.
Network Virtualization – with network virtualization, the network is “carved up” and can be used for multiple purposes such as running a protocol analyzer inside an Ethernet switch. Components of a virtual network could include NICs, switches, VLANs, network storage devices, virtual network containers, and network media.
Storage Virtualization – with storage virtualization, the disk/data storage for your data is consolidated to and managed by a virtual storage system. The servers connected to the storage system aren’t aware of where the data really is. Storage virtualization is sometimes described as “abstracting the logical storage from the physical storage.

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R.karthikeyan