Virtualization technologies have revolutionized the world of hosting and servers in general, by providing a very simple and effective way to provision or discard servers of almost any size, with unmatched scalability.

Cloud servers are extremely flexible and can accommodate almost any type of operating system, regardless of the one installed on the host.

There are many companies that offer commercial virtualization products today, but all of these actually rely on only a few core technologies. Virtual servers communicate with the host through a hypervisor, which operates as a link between the cloud and its hardware resources.

Today, most providers use one of the four main open source hypervisors available: KVM, XEN, vSphere (developed by VMware) and Microsoft’s Hyper-V. All of them have various strengths, but KVM hypervisors are the best overall, we will detail their advantages in this article.

KVM (Kernel Based Virtualization)

After Intel (VT-X) and AMD (AMD-V) implemented hardware virtualization support in their processors, Kernel based virtualization was developed to build on these features.

Today, it is maintained by Red Hat, the company that offers the most important Linux professional distribution, as well as the widely-used CentOS.

KVM hypervisors use a module built inside the operating system kernel that allows them to access the virtualization features of the CPU. The module was quickly adopted by the industry, and was included in the mainline Linux kernel since version 2.6.

This is a different approach from the one used by competing technologies. XEN for example doesn’t use the kernel at all and actually operates outside the host operating system, while other hypervisors emulate the CPU completely.

Through the kernel module, KVM machines have direct access to all the required basic services, such as process management, memory allocation, I/O operations and so on. This offers improved virtual server performance, as well as several key features not found in other hypervisors.

Every KVM virtual environment is fully isolated and secure, with its own resources and virtual hardware such as storage, graphics card or network adapter.

Advantages of KVM hypervisors

By working directly with the kernel, KVM has often been described as a bare-metal hypervisor. This translates in superior performance, when compared with other technologies using the same amount of hardware resources.

The direct access to resources also allows a very fast resizing of virtual machines, with only a minimal downtime required in order to adjust the number of CPU cores, the amount of RAM or disk storage space.

Virtual machines run as typical Linux processes, under the normal operating system environment. As a result, they provide the full set of features of the host system and support the latest technologies included in the Linux kernel, out of the box. For example, any file system supported by Linux can be configured on the virtual servers.

Working directly with the kernel also enables some very important security features. Security Improved Linux (SELinux) is active in all virtual machines, while communication between them is strictly controlled.

On top of that runs another security layer known as sVirt, which allows setting Mandatory Access Control Rules (MAC) to be applied to the virtual machines, with well-defined security boundaries and limits.

As a result, KVM hypervisors have earned some of the most difficult security certifications, including the Assessment Certification Level 4+ (EAL4+) required by the US government.

KVM hypervisors offer full control over the server and its hardware resources. This means that virtual machines can use any type of operating system, including custom kernels that are required by some applications.

Since the machines are fully isolated, any number of different kernels can run at the same time. The hypervisor is even able to emulate modern CPU features not supported by the actual processor. Containers, including Docker, are natively supported.

KVM servers also provide an API with rich options that allows machines to be remotely configured and provisioned. It is used by all major provisioning platforms, which have developed their own tools in order to offer even more options.

Another key advantage of a KVM VPS is the very quick migration time. Machines can be migrated both offline and online, without any risk of data loss and un-noticeable downtime. It is possible to migrate to a server with a different CPU architecture and even to channel it through and external service, such as ssh.

KVM machines are very flexible and additional virtual resources can be added live, as well as virtual PCI devices. It is also possible to adjust disk I/O at any time, without downtime.


A common disadvantage of choosing a KVM VPS is the higher price compared to other virtual servers with inferior features.

This is no longer an issue, since has just launched cheap KVM VPS plans that provide full performance at a very cheap price.

Our KVM plans have between 2 and 6 CPU cores and up to 12GB of RAM, with unmetered networks and both IPv4 and IPv6 addresses included. Need a custom solution? Contact us and we will be glad to help.