29. What is a snapshot?

A snapshot is a “point in time image” of a virtual guest operating system (VM). That snapshot contains an image of the VMs disk, RAM, and devices at

the time the snapshot was taken.  With the snapshot, you can return the VM to that point in time, whenever you choose. All changes made after the

snapshot was taken may be based on that snapshot information (incremental changes). You can take snapshots of your VMs, no matter what guest

OS you have and the snapshot functionality can be used for features like performing image level backups of the VMs without ever shutting them down.

Do not confuse Virtual Machine Snapshots with Microsoft’s VSS (Microsoft’s Volume Shadow Copy Service). Snapshots can be taken in just about

every virtualization platform available.

What is Quick Migration?

Quick Migration is a feature of Microsoft’s Hyper-V virtualization platform. With Quick Migration, you can move running virtual machines from one host

to another host server with minimal downtime. This feature is comparable to VMware’s VMotion except Quick Migration, in its current incarnation, is not

as quick as VMotion (VMotion is about 1 second vs Quick Migration of about 5-20 second)

What is a P2V conversion?

Virtualization is most frequently used for server consolidation. This is where physical servers are converted into virtual servers. This “physical to virtual”

conversion process is commonly called P2V conversion. This process can be done manually but it is easier if you use a P2V conversion application.

While this P2V (or Virtual machine Import) functionality may be built into the management interface for your virtualization product, there are also

standalone P2V products such as VMware Converter (diagram shown below) and Vizioncore’s vConverter.

These P2V products connect to the physical server, copy all data from that physical server into a virtual disk on the virtual server, replace the drivers in

the guest operating system with virtual drivers, and start the new virtual machine. In some cases, there is no downtime for end users of that server.

Similar to a P2V conversion, a V2V (virtual to virtual) conversion is where a virtual guest machine from one virtualization platform is converted to

another virtualization platform.

34. What is VDI?

VMware describes Virtual Desktop Infrastructure (VDI) as “delivering desktops from the data center”. In other words, VDI is where enterprise desktop

computers are virtualized, moved to the data center, then presented over the LAN or WAN to the end users. Once VDI is used, typically the end user

devices are replaced with thin-client devices.

While VMware has a VDI product called VDM (Virtual Desktop Manager), VDI is not a product exclusive to VMware. Other VDI vendors include Citrix

XenDesktop & Kidaro (now owned by Microsoft).

With VDI, virtual desktops are served by enterprise virtualization servers running products like VMware ESX, Microsoft Hyper-V, and Xen Server. With

the addition of the VDI products, these desktops can be dynamically created, pooled & shared, or even accessed from a GUI menu, over a web page.

The graphic below, shows some examples of how VDI could be used and how it works.

38. How many virtual machines can you run on one host?

As with many server performance questions, the answer to this question is “it depends”. You can run as many VMs on a single host as your hypervisor

supports (usually that is a lot) and as you have server resources for (RAM, CPU, Disk, and Network).

Typically, on a desktop PC, you can run 1-3 VMs and on a Server you can run 10-50 VMs – depending on the application demands