KVM vs OpenVZ Virtualisation: Why KVM is the Only Choice for Serious Hosting

Two Fundamentally Different Approaches

KVM (Kernel-based Virtual Machine) creates true virtual machines with complete hardware emulation. Each KVM guest has its own kernel, virtual hardware, and complete OS environment. OpenVZ creates containers that share the host server's kernel — all containers must use the same kernel version as the host.

Why Shared Kernels are Problematic

With OpenVZ, you cannot run a custom kernel, cannot use kernel modules not installed on the host, and cannot run applications that require kernel-level features unavailable in the host kernel. This eliminates Docker, many firewall configurations, WireGuard VPN, and numerous other tools from OpenVZ environments.

Resource Guarantees: The Critical Difference

KVM allocates hardware resources at the hypervisor level — your 8 GB of RAM is physically reserved for your VM. No other VM can consume it. OpenVZ uses a burst-able model where containers can consume more resources than allocated if the host has headroom, but can also be throttled when the host is under load.

Security Isolation

KVM provides hardware-level isolation. A compromised KVM guest cannot affect other guests or the host. OpenVZ container escape vulnerabilities have been documented — kernel exploits that break container isolation are significantly more common than KVM guest escapes.

Performance Comparison

KVM adds approximately 2-5% overhead compared to bare metal. OpenVZ containers run at near-native performance but with the resource unpredictability mentioned above. For most workloads, the security and isolation benefits of KVM far outweigh the minor performance difference.

FAQ

Can I run Docker in an OpenVZ container?

Not reliably. Docker requires kernel namespaces and cgroups that OpenVZ containers do not provide. At Power Down, all our VPS plans use KVM — Docker works perfectly.