KVM vs. OpenVZ

Category: VPS & Cloud · Updated 2026-11-01

KVM (Kernel-based Virtual Machine) is full virtualization, where each VPS runs its own independent operating system kernel, giving strong resource isolation and the freedom to run almost any OS. OpenVZ is container-based, OS-level virtualization where every VPS on a server shares the host's single Linux kernel, which is lighter on resources but limits VPS instances to Linux and generally gives weaker isolation and resource guarantees.

What KVM virtualization is

KVM turns the Linux kernel itself into a hypervisor, using hardware-assisted virtualization features built into modern CPUs. Each KVM-based VPS gets its own virtual hardware, its own independent kernel, and memory that is not shared with other VPS instances on the same physical host. Because each guest runs a complete, separate operating system, a KVM VPS can run practically any OS the virtual hardware supports, including different Linux distributions, Windows Server, or BSD variants.

What OpenVZ virtualization is

OpenVZ takes a different approach called OS-level virtualization, or containerization: every VPS (called a container in OpenVZ terminology) runs as an isolated environment on top of one shared Linux kernel owned by the host server. This avoids the overhead of booting a separate kernel per VPS, which lets a provider run more containers on the same hardware. The tradeoff is that containers cannot run a different kernel or operating system family from the host, so OpenVZ VPS instances are Linux-only, and custom kernel modules generally are not possible inside the container.

Side-by-side comparison

	KVM	OpenVZ
Virtualization type	Full virtualization, own kernel per VPS	OS-level virtualization, shared host kernel
OS flexibility	Linux, Windows, BSD and others	Linux only, tied to the host's kernel
Isolation	Strong, each VPS is self-contained	Weaker, VPS instances share kernel-level resources
Resource overhead	Higher, due to running a full separate kernel	Lower, allowing higher density per physical server
Custom kernel modules	Supported	Generally not supported inside the container

Why the difference matters when buying a VPS

Because OpenVZ containers share one kernel and can be packed more densely onto a physical server, OpenVZ-based plans have historically been offered at lower prices than comparable KVM plans. That density also means resource allocations on OpenVZ are more likely to be oversold or burstable rather than strictly guaranteed, so performance can be more affected by what other tenants on the same host are doing. KVM's per-VPS kernel generally makes resource guarantees more meaningful, though any provider, on either technology, can still oversell capacity if they choose to, so the hosting company's own policy matters as much as the technology itself.

How to tell which virtualization your VPS uses

The provider's product page or order form usually states the virtualization type directly, but it can also be checked from inside the VPS itself on most Linux systems:

systemd-detect-virt

This command typically prints "kvm" on a KVM-based VPS or "openvz" on an OpenVZ container, which is a quick way to confirm what you are actually running if a listing is unclear.

Frequently asked questions

Is KVM better than OpenVZ?

For most uses, KVM offers stronger isolation, more guaranteed resources, and far more OS flexibility, which is why it has become the more common choice for general-purpose VPS hosting; OpenVZ can still make sense where its lower overhead and lower cost matter more than those tradeoffs.

Can an OpenVZ VPS run Windows?

No, OpenVZ containers share the host's Linux kernel and cannot run a different operating system family, so Windows is not available on OpenVZ; a KVM-based VPS would be needed instead.

Why are OpenVZ VPS plans usually cheaper?

OpenVZ's shared-kernel design lets a provider run more containers per physical server than KVM's full virtualization allows, which generally translates into lower prices, though sometimes at the cost of less guaranteed resource isolation.

How do I check if my VPS uses KVM or OpenVZ?

Run the "systemd-detect-virt" command on most Linux systems, which reports "kvm" or "openvz" depending on which virtualization technology the VPS is running on.

Does OpenVZ share RAM between VPS instances?

OpenVZ containers are typically allocated a memory limit, but because they share the same kernel and underlying resources, memory management is less strictly separated than on a KVM VPS, which has its own independent kernel managing its own memory.

Is OpenVZ still commonly used today?

OpenVZ is less common than it once was, as KVM and lightweight container platforms like LXC have become more popular for general VPS hosting, though some budget-focused providers still offer OpenVZ plans.