KVM vs OpenVZ vs LXC: Which virtualization type to choose?

When you order a VPS server, you rarely read what type of virtualisation the provider uses. Yet this has a fundamental impact on what you can do with the server, how it is isolated from other users and what performance you actually get. This article explains the differences between the three most widespread technologies, KVM, OpenVZ and LXC, and will help you choose correctly.

Two basic models: Full virtualization versus containers

Before we move on to specific technologies, it is important to understand the basic classification. There are two approaches to sharing a physical server between multiple VPS instances:

Full virtualisation (KVM, VMware, Hyper-V) It creates complete virtual hardware, virtual CPU, virtual RAM, virtual disks, virtual network card. Each VPS runs on its own virtual machine with its own kernel. It is like having your own physical computer inside a physical computer.

Containerisation (OpenVZ, LXC/LXD, Docker) In contrast, they share the host system's kernel. Each container sees its own file system, processes and network interfaces, but all containers on one host share a single operating system and a single kernel. It is like having your own flat in a house. You share the load-bearing walls and utilities, but you have your own space.

KVM: Full virtualisation, maximum isolation

KVM (Kernel-based Virtual Machine) is currently the dominant technology for VPS hosting. It has been part of the Linux kernel since 2007 and is supported by virtually every modern processor (Intel VT-x, AMD-V).

What KVM offers

• Own kernel - each KVM VPS has full control over its kernel. You can upload a custom kernel, use kernel modules, and configure sysctl parameters without restrictions.
• Full insulation A bug, exploit or kernel panic on one VPS cannot affect other VPS instances on the same host.
• Any OS - any operating system can run on the KVM: Linux, FreeBSD, Windows Server, even NetBSD or OpenBSD.
• Dedicated RAM - memory is reserved exclusively for your VPS. The provider cannot "over-commit" memory at the expense of your performance (or if they do, it is disclosed).
• Consistent performance - because the kernel is not shared, performance is more predictable. An aggressive workload from another customer on the same host will not affect you as dramatically as with containers.

Disadvantages of VRF systems

Each VM requires memory reservation for the kernel, init system and basic processes: typically 50-100 MB more than a container. Consequently, fewer KVM VPS can be hosted on the same physical hardware than containers, which is reflected in the price. KVM VPS are generally more expensive than OpenVZ/LXC with comparable parameters.

OpenVZ: First-generation containers

OpenVZ is an older container technology that once dominated low-cost VPS hosting. It is tightly coupled with the Linux kernel, OpenVZ patches must be integrated directly into the kernel used by the host.

Advantages of OpenVZ

• Lower overheads - containers share a kernel, so memory usage is lower. More instances can be hosted on the same physical hardware.
• Quick start-up - the container starts up in seconds, the VM in tens of seconds
• Price - lower overhead for providers means lower prices for customers

Disadvantages of OpenVZ and why many providers are abandoning it today

• Shared kernel - you cannot load custom kernel modules, change kernel parameters, or use non-standard network stacks. Running Docker inside an OpenVZ container is problematic.
• Linux dependency - Windows or BSD cannot be started
• Overselling - providers on OpenVZ more easily "resell" RAM because the system allows virtual memory to be shared. Your "2 GB RAM" may be less in practice.
• Obsolescence - OpenVZ development is stagnant; the open-source version (Virtuozzo) has a limited community.

LXC/LXD: Modern containers at system level

LXC (Linux Containers) is a modern alternative to OpenVZ that does not require special kernel patches. It uses native Linux cgroups and namespaces. LXD is the management layer for LXC from Canonical (the creators of Ubuntu).

LXC vs OpenVZ

LXC offers better isolation than older OpenVZ, supports unprivileged containers (the container has no root access to the host) and integrates more effectively with modern Linux distributions. Proxmox VE, today's most popular open-source hypervisor for VPS hosting, natively supports both KVM VMs and LXC containers from a single interface.

Functions	KVM	LXC	OpenVZ
Own kernel	Yes	No	No
Kernel insulation	Full	Partial	Partial
Windows/BSD	Yes	No	No
Docker inside	Fully	With the setup	Problematic
Overhead memory	Higher	Low	Low
Price	Higher	Lower	Lowest
Development	Active	Active	Stagnating

Proxmox VE: Manager for both technologies

Proxmox Virtual Environment is an open-source platform for managing virtual machines and containers that today powers a large part of VPS hosting in Europe. From a single interface it manages both KVM VMs and LXC containers, offers live migration, HA clustering and integrated backups.

If you are interested in what your provider uses "under the hood", Proxmox with KVM is today's gold standard for serious VPS hosting. It allows providers to offer both KVM VPS (full isolation) and LXC containers (lower price) from a single infrastructure.

What Exascale.cz uses and why

Exascale.cz operates exclusively KVM virtualization on Proxmox VE. This decision is based on several principles:

• Guaranteed insulation - No customer can affect the performance of another customer sharing the same kernel. KVM ensures strict boundaries for CPU, RAM and I/O.
• Flexibility for customers - On a KVM VPS you can run Docker, Kubernetes, custom kernel modules and VPN servers (WireGuard, OpenVPN) without restrictions. With OpenVZ/LXC, many of these use cases would require special configuration or might not be possible at all.
• Honest Specifications - RAM is always dedicated, with no overselling. 4 GB RAM in the offer = 4 GB available to your system.

When to choose a container over a KVM VM

Containers (LXC) have their place. They are not a bad technology, just a different one. They make sense for:

• Development environment - fast startup, low overhead, easy cloning. Developers who need dozens of identical environments for testing will appreciate LXC.
• Microservices - for orchestrating containers with Kubernetes or Docker Swarm, it is better to use KVM VMs and run the containers inside them
• Internal infrastructure - if you run your own Proxmox cluster and know what you're doing, LXC containers for internal services (DNS, monitoring, load balancer) are an efficient choice

For production VPS accessible to customers or external users, KVM is always the safer choice in terms of isolation and predictable performance.