The Great Virtualization Debate: OpenVZ vs. Xen/KVM
It is 2011, and the VPS market is flooded. You can find a Virtual Private Server for the price of a latte in Oslo. But as any sysadmin who has spent a Friday night debugging inexplicable latency knows, there is no such thing as a free lunch. If you are paying peanuts, you are likely sharing your kernel with three hundred other users on an overloaded node.
At CoolVDS, we often handle migration requests from clients fleeing budget providers. The story is always the same: "My site is down, but the host says the server is up." The culprit? Almost always OpenVZ resource contention.
Understanding the Architecture: Containers vs. Hypervisors
To make the right choice for your infrastructure, you need to understand what lies beneath the shell.
OpenVZ: The Shared Kernel Approach
OpenVZ is operating system-level virtualization. It relies on the Linux kernel to split the physical server into multiple "containers" (VEs). Think of it like an apartment complex: you have your own walls, but you share the plumbing, the heating, and the foundation.
The Pros:
- Efficiency: Less overhead means more RAM for your applications.
- Burst Resources: If the node is idle, your container can use extra CPU cycles.
- Instant Upgrades: Changing resource limits happens on the fly without a reboot.
The Cons:
- The "Noisy Neighbor" Effect: If one user on the node gets hit by a DDoS or runs a heavy intricate MySQL query, your I/O performance tanks.
- Kernel Limitations: You cannot run your own kernel. Need a specific module for IPtables or complex VPN routing (TUN/TAP)? You are at the mercy of the host's configuration.
- Overselling: This is the dirty secret of the hosting industry. Providers can easily pack 100GB of RAM worth of customers onto a 32GB server, betting that not everyone will use it at once.
Xen & KVM: True Hardware Virtualization
Technologies like Xen (PV/HVM) and the rapidly maturing KVM (Kernel-based Virtual Machine) offer strict isolation. This is like owning a detached house. You have your own kernel, your own swap space, and strict memory fences.
The War Story: The Magento Mystery
Last month, a client brought us a Magento 1.5 e-commerce store hosted on a budget OpenVZ VPS. During traffic spikes, Apache would segfault, and MySQL would vanish.
We checked the logs. The memory usage seemed fine inside the container (free -m), but the application kept crashing. The smoking gun was in the OpenVZ-specific proc file:
cat /proc/user_beancounters
We looked at the privvmpages failcount. It was skyrocketing. The host had set a "Burst Limit" that looked generous on paper, but a "Guaranteed Limit" that was tiny. When the physical node got busy, the host brutally killed the client's MySQL processes to reclaim memory. That is not a platform for business; that is a lottery.
Why KVM is the Future (and the Standard at CoolVDS)
While OpenVZ has its place for lightweight testing or DNS servers, CoolVDS bets on KVM for production workloads. With RHEL 6 pushing KVM as the default virtualization technology, the writing is on the wall.
Pro Tip: If you must use OpenVZ, monitor your 'failcnt' column in/proc/user_beancounters. If you see numbers increasing there, your provider is throttling you, regardless of whattopsays.
| Feature | OpenVZ | KVM (CoolVDS) |
|---|---|---|
| Kernel | Shared | Dedicated |
| Overselling Risk | High | Low (Strict RAM allocation) |
| Disk I/O | Shared/Unpredictable | Dedicated/Stable |
| OS Support | Linux Only | Linux, BSD, Windows |
Data Integrity in Norway
For our Norwegian clients, stability isn't just about uptime; it's about compliance with the Personal Data Act (Personopplysningsloven). When you share a kernel, theoretical exploit vectors exist that could allow memory leakage between containers. While rare, it is a risk a bank or a health institution cannot take.
Running on CoolVDS KVM instances in our Oslo datacenter ensures that your data remains strictly isolated. Plus, with the low latency to the NIX (Norwegian Internet Exchange), your SSH sessions feel like you are typing on the local machine.
Conclusion
Don't let a budget virtualization platform jeopardize your project. If you are running a static HTML site, OpenVZ is fine. But for databases, Java applications, or anything that requires consistent performance, you need hardware isolation.
Ready to stop fighting for CPU cycles? Deploy a pure-performance KVM instance on CoolVDS today. Experience true isolation and the speed of our new SSD-cached storage arrays.