OpenVZ vs. Xen: The Truth About Container Virtualization

Let’s be honest. If you have been browsing WebHostingTalk lately, you have seen the race to the bottom. Providers offering 512MB RAM VPSs for ridiculously low prices. Almost invariably, these are built on OpenVZ. But when your MySQL database starts crashing because a neighbor on the same node decided to compile a kernel or run a fork bomb, that cheap monthly fee becomes the most expensive mistake in your infrastructure.

I have spent the last week migrating a client's high-traffic vBulletin forum from a budget US host to our infrastructure here in Oslo. They were plagued by random sluggishness. The culprit? failcnt.

The Architecture: Containers vs. Hypervisors

To make an informed decision for your deployment, you need to understand what is happening under the hood.

OpenVZ is operating system-level virtualization. It relies on the Linux kernel of the host node. There is no hypervisor layer translating instructions. All containers (VEs) share the same kernel version. This means zero overhead, which is fantastic for raw throughput, but it introduces a critical weakness: lack of isolation.

Xen (paravirtualization), on the other hand, allows you to run your own kernel. It reserves physical RAM and CPU slices. If a neighbor panics their kernel, your instance keeps humming along.

Pro Tip: If you are running OpenVZ, check your limits immediately. Run this command: cat /proc/user_beancounters If the last column (failcnt) is anything other than 0 for privvmpages or kmemsize, your provider is squeezing you, and your applications are silently failing memory allocations.

The "Noisy Neighbor" Reality

In the hosting market, OpenVZ is often synonymous with "overselling." Because the file system and memory are shared, a provider can fit 100 users on a server that should only hold 50, betting that not everyone will use their resources at once. When they do, the node crawls.

At CoolVDS, we take a different approach to OpenVZ. We treat it as a performance tool, not a density tool. By enforcing strict User Bean Counter (UBC) limits and maintaining low contention ratios on our RAID-10 SAS arrays, we ensure that the inherent speed advantage of OpenVZ isn't lost to I/O wait times.

Comparison: When to Use What

The Compliance Angle: Data in Norway

Beyond raw performance, we have to talk about jurisdiction. With the Personopplysningsloven (Personal Data Act) and the EU Data Protection Directive being strictly enforced by Datatilsynet, knowing where your data lives is non-negotiable. Hosting on a budget node in Texas might save you five kroner, but it exposes you to latency issues and legal grey areas regarding data transfer.

Our datacenters connect directly to NIX (Norwegian Internet Exchange). If your customer base is in Scandinavia, latency matters. We are seeing ping times to major Norwegian ISPs drop from 30ms (continental Europe) to under 2ms (Oslo local). For a chatty application or a database-heavy site, that latency reduction is more valuable than adding more RAM.

Optimizing Your Container

If you are committed to OpenVZ, you must optimize for the environment. You cannot just drop a standard my.cnf file in and hope for the best. InnoDB buffer pools must be calculated against your privvmpages limit, not the total visible RAM, or MySQL will be killed by the OOM killer instantly.

# /etc/my.cnf optimization for 512MB VPS
[mysqld]
key_buffer = 16M
query_cache_size = 8M
innodb_buffer_pool_size = 64M
thread_cache_size = 4

Final Verdict

OpenVZ is not the enemy. Bad configuration and greedy hosting practices are. If you need a lightweight web server or a development sandbox, OpenVZ provides unmatched price-to-performance ratios. However, if you need to load specific IPTables modules for a VPN, or you need absolute guaranteed I/O for a busy database, you should be looking at our Xen or emerging KVM solutions.

Don't let your infrastructure be a gamble. Whether you choose the raw efficiency of containers or the isolation of Xen, ensure your host isn't cutting corners on the hardware backend. Deploy a test instance on CoolVDS today and see what proper resource allocation feels like.