In recent years, virtualization has advanced beyond server and application virtualization to include the virtualization of operating systems. One of the most popular techniques in the market today is Virtual Desktop Infrastructure (VDI). Ardence, a company now part of Citrix, pioneered the Operating System (OS) Virtualization concept. This tutorial will provide an introduction to the fundamentals of OS virtualization.
What is OS Virtualization?
An operating system does not come pre-installed with virtualization and does not require a hard disk drive. Instead, everything is run from the network using a virtual disk. This virtual disk obtains the disk image file from a remote server through the current implementations.
Types of Virtual Disks
There are two categories of Virtual Disks in the majority of implementations:
- Private Virtual Disk: A private virtual disk is typically reserved for use by a single user, much like a local hard disk. The user can store data on this virtual disk depending on the permissions assigned. When the client restarts, the settings are preserved, just as when using a physical local hard disk.
- Shared/Common Virtual Disk: Multiple clients require access to a shared Virtual Disk simultaneously. While in use, any changes made to the disk are temporarily saved in a special cache memory. However, this cache gets cleared whenever a client shuts down or restarts. The creation of a Virtual Disk involves the use of an imaging technique.
How Does OS Virtualization Work?
The OS Virtualization server is the central point of the OS Virtualization structure. Its primary responsibility is to stream data to virtual disks for the client. Additionally, it determines which client will be connected to which virtual disk using a database that stores this information.
On the other hand, a client needs to contact the server to connect to the virtual disk and request components stored on the virtual disk to run the operating system.
Connecting to OS Virtualization as a Server
To start the machine, you must connect with the OS Virtualization server. Most products offer different methods for connecting to the server. One commonly used method is through a PXE service, while a bootstrap is also used frequently. Regardless of the method, the Network Interface Card (NIC) is initialized, receives a DHCP-oriented IP address, and is linked to the server.
What Happens at Virtual Disk Connection?
Once the connection between the client and the server is established, the server checks its database to determine if the client is known and which virtual disks need to be assigned. A boot menu is displayed on the client if more than one virtual disk is connected. If only one disk is set, it will be connected to the client later.