Understanding the Difference Between OpenVz and KVM

In the last few years, virtualization has become a popular option for many companies, due in large part, to its ability to increase productivity, while reducing infrastructure costs. There are multiple virtualization technologies available for companies to run their daily operations. With the surge of companies looking at private servers, it’s important to consider the options before making a choice.

Two important options to consider are OpenVz and KVM (Kernel-based Virtual Machine) — virtualization and containerization software for Linux. Both offer a host of benefits and are often measured against each other when companies are making their choice. In this article, we’re going to look at what makes them different. But before we do that, let’s look at some basics first.

What is Virtualization?

To put it succinctly, virtualization technology allows a single system to run multiple infrastructures simultaneously. How? By installing a software known as the hypervisor, which creates and runs different virtual machines on a single host computer. Each virtual system, or machine, is self-operating and independent. This means that software running on one particular system does not have access to configure or impact the resources given to another. Many VPS Hosting providers use hypervisors that are installed on their physical servers and offer independent sections to individual users as Virtual Private Servers.

The hypervisor forms a thin layer of separation between each machine and the host. It also manages these Virtual Machines, by allocating a part of the host computer’s resources, such as memory, CPU and hard disk.

What is Containerization?

This is a different concept from virtualization. In this scenario, instead of using a hypervisor, an OS is installed on the system and containers are created. Inside these containers, companies can run independent applications and the operating system handles the resource allocation to each individual container. In this system, the underlying kernel and drivers are shared amongst all containers. This approach depends heavily on the OS and can only run programs that are compatible with it.

Now, let’s look at KVM and OpenVz independently.

Kernel-based Virtual Machine

KVM (Kernel-based Virtual Machine) is an open source virtualization technology for Linux. It uses a type 2 hypervisor (a virtual machine manager, which is installed as a software application on an existing Operating System). It resides within the Linux Kernel (the centre of the OS, which provides basic serves for other parts of the OS). In KVM, the Linux Kernel acts as the hypervisor — streamlining the management and improving the performances of the virtual machines. Since 2007, KVM has been bundled with the Linux OS and can be installed with the Linux Kernel. KVM allows for multiple guest OS’, including Windows, Haiku and Solaris and more.

OpenVz (Open Virtuozzo)

OpenVz is an operating system level virtualization technology for Linux. This virtualization solution was created by Virtuozzo (a private software company) in 2000 and was made open source in 2005 (hence the name, Open Virtuozzo). OpenVz creates multiple, secure and isolated Linux Containers (also referred to as Virtual Private Servers and Virtual Environments) on a single physical server. Each container acts as a stand-alone server.

What is the difference?

Companies who are looking at purchasing a VPS will often compare and contrast these two options that hosts offer. That process involves examining the differences between them. That’s what we’re going to do with OpenVz and KVM.

To begin with, the biggest difference between KVM and OpenVz is that OpenVz only hosts Linux Operating Systems. KVM, on the other hand, is a lot more flexible in this regard. As we’ve mentioned earlier, numerous guest Operating Systems can work with KVM (by using virtualization extensions to connect to them).

Secondly, OpenVz allows you to share the resources, like RAM, completely. This is how it works. OpenVz uses a shared kernel with a thin layer of virtualization on the Operating System (Linux). The kernel remains open to all VPS users on this particular node and therefore remains fixed — that is, users cannot customise it. Once companies have used up their allocated RAM, the remaining users of the server can use it. This is fine for small applications, however, companies that are running resource heavy applications may run into some problems.

In contrast, KVM allows its users to allocate values to their resources. That way applications only use the resources that they need. This means companies can perform at high capacity with lower needs from the hypervisor. Each individual gets a dedicated 100 per cent RAM, CPU and storage. As a result, KVM offers its users an isolated environment and users are given their own kernel.

Overselling

A rampant problem these days, that many companies encounter, is overselling. This is especially true for OpenVz systems, where companies can end on a system that has too many containers. This means OpenVz might be available at a cheaper price, but there is always the risk of overselling to be kept in mind.

Final thoughts

Companies that are looking for scalability and speed can look at OpenVz as an option. KVM, on the other hand, provides virtualized hardware as well as guaranteed resources. KVM suits the purposes of game servers, resellers and small to medium-sized businesses. Additionally, KVM offers you the chance to use a different OS and a more advanced Linux kernel. It all depends on what each company needs, to fulfil their specific requirements. Choose wisely, and it will serve you well.