“Which virtualization is better for internet servers, KVM or OpenVZ?” This question comes up often when a customer is searching for buy a Virtual Private Server. What a client should do first is to consider the amount of RAM and disk space he/she needs, then look into which virtualization technology web hosting company offers. There are many technologies in the market like Hyper-V, Xen, VMware, let’s speak about more frequent types: KVM and OpenVZ.
Differences Between KVM and OpenVZ
First of all, the most basic difference between OpenVZ and KVM is that OpenVZ can ONLY host LINUX operating systems, while KVM is more flexible and can host Linux, Windows, and custom OS.
Both a pro and a con of OpenVZ is the complete sharing of resources it allows. OpenVZ uses a shared kernel with a layer of virtualization on top of the actual Linux OS. Since this kernel is shared by all VPS users on this node, the kernel is not customizable. Once you have hit your allocated RAM provided to you by the host, the remaining RAM becomes a free-for-all for users on the server. This is not a problem if you run small applications, but you may be in trouble if you are running something more resource intensive.
KVM allows you to set maximum and minimum values to your resources, providing you to use only the resources your applications need. This is true, real hardware virtualization, meaning better performance from lower requirements on the hypervisor. 100% of the RAM and disk resources are dedicated to one individual user. KVM provides a more isolated environment and gives users their own kernel.
The risk of overselling: Overselling is where a host will overcommit resources to certain accounts hoping that not every account uses up all those resources. While everything can be oversold, beware of shady hosting companies overcommitting OpenVZ systems and putting you on a system with too many containers. KVM can also be oversold, but it’s better isolated. Since OpenVZ hosts are often oversold, OpenVZ servers are typically a cheaper cost than KVM servers.
OpenVZ provides the end-user with speed and scalability, and it’s more affordable. KVM offers private virtualized hardware including network card, disk and graphics adapter, and guaranteed resources for increased reliability and customizability. KVM packages are ideal for serious resellers, game servers, small businesses, and medium-sized enterprises.
NOTE: If you are a host selling to your clients, OpenVZ is easier to set-up and maintain properly, while KVM takes much more networking knowledge. OpenVZ and their templates are more beginner friendly in that aspect. If you are simply an end-user, don’t worry and go with a managed hosting provider.