Cloud has become a broad term used to describe various products and services, which is supposed to be utilizing the distributed computing model. Strictly speaking “Cloud Server” is just a virtualized computer instance, a Virtual Private Server. However the term “Cloud” should mean that a “Cloud Server” is a computing instance created on top of an IT infrastructure in which the processing power (processing nodes) – CPU and RAM for example – reside on different physical machines than the data storage (SAN or storage nodes).

Some companies define “Cloud Server” for example as “on-demand virtual machine, created to deliver customizable performance and reliability”, although this is pretty much marketeer’s language. Please also be advised that billing a any virtual server hosting service (whatever it is labeled) on per minutes, per hour or per day basis doesn’t make it “Cloud”. What makes it a “Cloud Server” is the ability to scale up the allocated computing resources on demand.

To understand term “Cloud Hosting”, please read article “What does a Cloud Hosting Mean?“

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.