Virtual Private Servers
Virtualization is a major technological leap in internet industry. It has proved to be a powerful technology to simplify software development, testing and to enhance data centre quality.
Increased manageability and flexibility provided by Virtualization to IT environments gave it a powerful lead over other technologies.
Virtualization through a combination of Hardware-assisted technology and software-based solutions provide maximum system utilization by consolidating multiple environments into a single server.
Virtualization techniques can be mainly classified as:
l Full virtualization
l Para-virtualization
l Operating System assisted Virtualization
l Hardware-assisted virtualization
Full virtualization:
This is the ideal virtualization technique in which the guest OS is fully abstracted from the underlying hardware by the virtualization layer.
The guest OS is not aware of it being virtualized and requires no modification. Full virtualization is the only option that requires no hardware assist or operating system assist to virtualize sensitive and privileged instructions. The guest OS executes on the VM just as they would on a physical system.
For example: Microsoft Virtual Server and Vmware ESX Server are examples of full virtualization
Paravirtualization:
Para-virtualization attempts to provide most services directly from the underlying hardware instead of abstracting it. Para-virtualization provides near-native performance.
In this technique, it is possible to use different guest Operating Systems like Microsoft 2003/XP, RHEL, CentOS, Suse etc on the virtual servers.
For example: The open source Xen project is an example of paravirtualization. VMware has used certain aspects of paravirtualization techniques.
Operating System Level Virtualization:
In OS system level virtualization, kernel of the host OS allows for multiple isolated user-space instances. These user space instances are often called as containers, VE, or VPS. Owners of these user instances feel as a real server.
This form of virtualization usually imposes little or no overhead. It also does not require hardware assistance to perform efficiently.
For example: OpenVZ is an operating system-level virtualization technology based on the Linux kernel and operating system. OpenVZ allows a physical server to run multiple isolated operating system instances.
Parallels, Inc developed their proprietary software called Parallels Virtuozzo Containers based on OpenVZ.
Hardware Assisted Virtualization:
Intel (Intel VT) and AMD’s (AMD-V) hardware assist features released are the first step in hardware assisted virtualization that enabled removing the need for hypervisors to employ binary translation and OS-assisted processor
paravirtualization.
For example: Hardware-assisted virtualization is also known as accelerated virtualization; Xen calls it hardware virtual machine (HVM), Virtual Iron calls it native virtualization.
