Colocation is a term used to describe a certain type of IT Hosting service provided by telecommunication facilities and data centers to clients who own equipment and need to house it. There are different levels of Colocation – from colocation of a single standard desktop computer or rack server to rack enclosures (cabinets) used for colocation of multiple computing appliances.

The minimum services provided by the host facility (data center) to a client are: space, power feed, access to internet service, power and cooling. The facilities usually house IT equipment into rack cabinets (See “Server Cabinet”, “19-inch Rack” and “Tower Server Rack”), mount them into rack units, connect them to special types of power distribution units (PDU) and connect them to networking equipment (network switches) to provide them with Internet connectivity.

OpenVZ Hosting refers to a Virtual Private Server created through OpenVZ operating system-level virtualization (OS Virtualization) technique. OpenVZ virtualization is based on the Linux kernel and Operating System. OpenVZ allows anyone to to run multiple isolated operating system instances (also called “Containers”) on single physical web server. Those instances are called Virtual Private Servers (VPS) or Virtual Environments (VEs). VPS is definitely more popular term however.

OpenVZ virtualization technique is the basis of the popular commercial virtualization software Virtuozzo Containers owned by Parallels Inc. OpenVZ is licensed under the GPL version 2. It is also supported and sponsored by Parallels. The company does not offer commercial support for OpenVZ however.

Unlike other familiar virtualization technologies like Xen or Kernel-based Virtual Machine, the OpenVZ requires requires both the host os on the underlying physical server and Virtual Private Servers which run on top (guest OS) to be Linux. The VPS users can use different Linux OS distributions in their virtual instances. The VPS users can not run Windows or MacOS for example on a Linux based OpenVZ host server. Such machine requires reboot if the virtual environment processes get I/O hangs.

There is a certain performance advantage of OpenVZ based VPS compared to other form of virtualization. OpenVZ website says that, there is “only a 1–3% performance penalty for OpenVZ as compared to using a standalone server”.

OpenVZ is not considered as a “true virtualization” but as a technique that creates isolated containers (like FreeBSD Jails does). Other virtualization technologies like Xen, Kernel-based VM or VMWare virtualize the entire underlying server and allow the users of the Virtual Machines to run Operating systems (OS) different from the one of the physical machine. OpenVZ uses a single patched Linux kernel and therefore can run only Linux. However because it doesn’t have the overhead that a hypervisor do, and that’s it is considered as quite fast and efficient. The disadvantage is that all VPS function with the kernel version of the underlying physical server. Among other advantages is easy to allocate the unused RAM to any of the virtual servers, something which is not possible with full virtualization techniques.

OpenVZ based server system and the host VPS use a common file system. Each VPS instance  is a directory of files which is isolated using chroot. The new versions of OpenVZ also allow the container to have its own file system. Any VPS can be cloned by just copying the files in one directory to another and creating a config file for the VPS.

To find out more about OpenVZ, please visit http://wiki.openvz.org/Main_Page.