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OpenVZ and KVM Virtualizations: Main Differences

Both, OpenVZ and KVM virtualizations are incredibly popular among VPS users and, in fact, both can offer unique benefits and features. To choose one or another, first, it is highly recommended to take into consideration the VPS needs, because both virtualizations provide different applications and flexibility while managing a virtual server. For one to make the right decision, we suggest taking a look at the comparison and overview.

Photo Credit: Redswitches

What is KVM Virtualization?

KVM (Kernel-based Virtual Machine) is a technology dedicated to Linux kernel. Using it, multiple – Windows and Linux – virtual machines (VMs) can run side by side on the same hardware. Different from OpenVZ, KVM has isolated dedicated recourses. It’s important to note that each machine has private hardware: own graphics adapter, memory, network card, and kernel. Therefore, it acts independently: the machine will perform on its own without any interference by other virtual servers.

The main benefits of KVM:

  • Multiple virtual machines;
  • Separate graphics adapter, network card, memory, virtual disk;
  • Virtualization of any OS (Linux, Windows, etc.);
  • Configuration of a VPN server;
  • Dedicated resources.

To understand the overall view of both virtualizations better, the other should be discussed accordingly.

OpenVZ Virtualization

Compared to KVM for Linux kernel, this virtualization is based on the Linux container and can only run Linux. Despite that, similarly to KVM, it also allows dividing Linux servers into isolated VPSes. Instead of multiple apps on a server, the virtualization allows creating private Linux containers on a single physical server so server resources and the removal of possible software conflicts between processes are utilized in a different way. Each container is like a dedicated server with its own apps, users, files and IP address. 

The benefits of OpenVZ:

  • Pre-installed OSes;
  • Online backups;
  • Small resource consumption from the OS;
  • Containers share the same architecture and kernel version.

Because of different features, first, it is recommended to evaluate the expectations and needs of a VPS.

Technical features of KVM and OpenVZ Virtualization

The virtualizations also feature different technical characteristics that should be taken into consideration when choosing the most suitable one.

Key features of KVM include:

  • CPU/PCI hotplug support.
  • Vmchannel.
  • Migration.
  • Nested Guest.
  • KVM paravirtual clock.

Based on the above-mentioned characteristics, KVM enables communication channel between the guests and the host, move machines between nodes, run virtual machines within other virtual machines and more. Meanwhile,

OpenVZ offers:

  • I/O scheduler.
  • Fair CPU scheduler.
  • User beancounters.
  • Checkpointing and live migration.

Having an overview of both virtualizations based on their benefits and key features, it is time to compare them in a closer manner.

The comparison

One of the main differences between the virtualizations is that one supports only Linux systems while in the other (KVM) can be installed Linux, Windows and other custom OS versions. To compare the memory distribution, the memory not used by one container can be used by others in OpenVZ. On the other hand, KVM has a hard memory limit, thus providing stable resource distribution. Lastly, KVM VMs (virtual private machines) run on different kernel versions while the other virtualization shares the same kernel version and architecture.

Being completely different, each virtualization is best in different circumstances. KVM virtualization is designed for isolation and privacy, so it is the best choice when one needs total isolation between servers and total security with a slow deployment of the apps. On the other hand, if there is no security risk involved between the apps,  OpenVZ can offer fast apps deployment.

No matter which virtualization is chosen, both of them can offer great benefits for a VPS. The most important thing is to decide what is the purpose of your virtual server: if it‘s dedicated to a website or email hosting, consider virtualization technology for Linux. If you have a project with specific server configurations, take a deeper look into the KVM.

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