KVM (Kernel-based Virtual Machine) is a full virtualization solution for hardware containing virtualization extensions (Intel VT or AMD-V). It consists of a loadable kernel module that provides the core virtualization infrastructure.
KVM runs on top of the bare metal itself, as opposed to OpenVZ, which runs directly against the bare metal. While this might seem like a strong aspect while choosing KVM, there is more to it than you might think. Neither of them is outright better than the other, but one may be more preferable depending on your needs and applications that you are going to use.
Using KVM, one can have Linux and Windows virtual machines running side by side on the same hardware. Each virtual machine has private virtualized hardware: own kernel, a network card, disk, graphics adapter, etc. Since it has its virtualized hardware, the virtual server will act completely on its own.
Because KVM maintains separate instances for each virtual server, it uses more resources than OpenVZ from a host perspective. However, it gives a lot more isolation and customizability for users.
You can run Windows Server, Linux, or other OS.
KVM provides custom kernel modifications, patches, specific kernel versions, or obscure features that are not supported in OpenVZ.
Advanced Netfilter firewall configurations, e.g., ipset or nfnetlink.
If you want to add more CPU, RAM, disk space, bandwidth, or other resources, a reboot is necessary.
KVM is a tad bit more complex than OpenVZ, thus it is used by tech-savvy users or developers that know exactly what they are doing.
OpenVZ ease of use at a cost?
OpenVZ is an operating system-level virtualization technology, which allows a host operating system to be partitioned into containers with resources assigned to each instance within it. This means that each container shares the same underlying operating system but still operates as a secure, isolated Linux container.
Each container performs and executes exactly like a stand-alone server – a container can be rebooted independently and have root access, users, IP addresses, memory, processes, files, applications, system libraries and configuration files. This way, you can use the resources more efficiently, but at the same time, you can not run different OS types (Linux and Windows) as OpenVZ virtualization shares the same kernel between multiple containers.
Burst! What is that?
In OpenVZ, there are two types of resources, dedicated and burst. While dedicated resources are ones that the VPS is guaranteed to get if requested and you can call them “yours”, burst resources come from the remaining unused capacity of the system.
In such a scenario, the system may allow one VPS to borrow resources like RAM from another VPS when the second one is not using them. Since it is borrowing, such resources have to be returned as soon as possible if the other VPS requires their dedicated resources back, which means that your processes might become unstable or terminated in the run…
Good performance and fewer resources needed for the host compared to KVM.
For the end-user, it often comes with predefined templates that are easily installed.
Rebootless upgrades – there is no need to reboot the system if changes are made to the kernel, disk, or memory.
However, it is not easy to migrate to other platforms.
Also, you cannot use custom kernels because all the containers share the same kernel.
When choosing between the different virtualization techniques, there is no better choice than evaluating your needs and picking one solution that best fits your case. It might be an OpenVZ virtualization solution that best fits your needs, on the other hand, you might need a KVM powered service.
The main question is, “What are you going to do with the server?”
With OpenVZ, you can upgrade your plan (e.g., to get more memory or disk space), and you will instantly have your new system resources without rebooting.
On KVM, you will need to reboot your virtual machine for the change to take effect.
OpenVZ only supports Linux.
KVM can operate Linux as well as other operating systems such as Windows or BSD.
OpenVZ runs many containers using a shared kernel. Having a shared kernel gives a slight performance advantage as there is no overhead from running a kernel within a kernel.
KVM requires a running kernel inside the VPS if you need control of your own kernel, you should opt for KVM. For example, you might need to modify or patch the kernel.
OpenVZ is simpler and is easier to manage as a result.
KVM has many more options and settings, which can cause complications for inexperienced users.
Pick whichever option is more appealing to you and choose from our OpenVZ and KVM solutions!