Xen vs OpenVZ

What Is a VPS?

A virtual private server (VPS) is a method of splitting a physical server into several virtual servers that have their separate virtual environment. Each virtual server can run its own operating system, and each server can be independently rebooted.

Main features of a VPS

• Enables you to install any software (excluding the software mentioned in our AUP as prohibited) and have any kind of custom configuration.

• Guaranteed minimum of resources (memory, processor time and so on)

• Allocation of personal IP addresses

• Possibility of filtering rules and routing tables

Currently, a VPS is an excellent bridge between shared hosting plans and dedicated solutions allowing its user to save money and to have much more independence.

This technology has become possible with the invention of virtualization. It is a method of separating hardware from a single operating system. Each virtual machine called ‘guest’ is managed by a Virtual Machine Monitor (VMM), also known as a hypervisor. As the virtualization agent VMM is located between the guest and hardware, it can control the guests’ use of CPU, memory and storage.

Types of Virtualization

• Operating system level virtualization (OpenVZ)

• Full virtualization (Xen)

OpenVZ is an operating system-level virtualization technology based on the Linux kernel and is actually an operating system. OpenVZ allows a physical server to run multiple isolated operating system instances, known as containers, Virtual Private Servers (VPSs), or Virtual Environments (VEs).

Xen allows several guest operating systems to be run on the same computer hardware concurrently. It uses a form of virtualization known as full virtualization. Xen gives you much of the dedicated server behavior.

OpenVZ Technology

• Burstable and Guaranteed RAM

Guaranteed RAM – the amount of RAM dedicated to your virtual machine.

Burstable RAM – the amount of RAM shared between virtual machines on a VPS carrier. Can be used by your VPS if no one else uses it.

Good: You have some additional RAM available at load peaks.

Bad: It may not be fully available for your VPS, if other virtual machines experience peak load at that time.

• HDD subsystem is divided between VMs on a software level

Each virtual machine is sensitive to other virtual machines’ activity. You are not as dependent on other users as on a shared server, but still VPSes, to some extent influence each other’s performance.

• One guest operation system; the architecture is carrier-dependent

Only Linux OS can be installed:

CentOS (the only compatible with cPanel) 
Fedora 
Debian
Ubuntu 
OpenSUSE 
Gentoo

XEN Technology

• Guaranteed RAM + SWAP

If you run out of RAM, you use virtual memory, which stores the program data on hard disk. Unlike oVZ, you don’t have any ‘shared’ memory, all RAM you have according to the plan is always yours. But reading from disk is slower than reading from RAM, so it may slow everything down.

• HDD subsystem is divided on hardware level

Processes are scheduled on VM level and then re-scheduled on the carrier level. This way we don’t have all tasks from all VPSes lined up in one queue. A VPS can overload itself, but will not influence the whole carrier, i.e. XEN VPSes are more isolated and behave much like a dedicated server.

• Almost any OS can be installed

We currently work mostly with the same OS as for oVZ plans + FreeBSD and Windows.

Conclusion

Virtual Private Server (VPS) is a bridge between shared server and dedicated server.

Xen and oVZ use different types of virtualization technology.

What does this mean to a user?

• oVZ based VPS is a virtual machine virtualized on a software level. It is more isolated than an account on shared server and offers root access; only Linux OS can be installed

• Xen based VPS can be considered a “semi-dedicated server”, virtualized on a hardware level, more suitable for resource intensive activities compared to oVZ (streaming, for instance) with the ability to install any OS, including Windows.