The Truth About Your Virtual Private Server
It is 03:00 CET. Your Nagios alert just woke you up. Your MySQL service on the VPS is flapping, but when you SSH in, top shows load average is low. You check the memory, and it looks free. Yet, the site is crawling. Welcome to the world of OpenVZ overselling.
In the Norwegian hosting market, price wars are driving providers to cram as many containers as possible onto a single physical node. While OpenVZ (Open Virtuozzo) is a brilliant piece of engineering for density, it is frequently misused. As a systems architect who has migrated dozens of clients from sluggish budget containers to proper dedicated resources, I'm going to walk you through what is actually happening inside that black box.
The Architecture: Containers vs. Hypervisors
To understand the performance issues, you must understand the kernel. In hardware virtualization (like Xen HVM or the emerging KVM technology), every Guest OS has its own kernel. If your neighbor kernel panics, your server stays up.
OpenVZ is different. It is OS-level virtualization. There is one kernel—the host node's kernel. Your "server" is just a chroot environment on steroids with resource limits applied.
The Pros: Why We Still Use It
OpenVZ isn't inherently bad. In fact, for specific use cases, it beats Xen:
- Efficiency: There is almost zero overhead. A system call in the container is a system call on the host.
- Scalability: You can resize RAM and disk on the fly without a reboot. Try doing that with a physical server.
- Cost: Because we can run more instances on our Nehalem Xeon chassis, the cost per unit is lower.
The Cons: The "User Beancounters" Nightmare
Here is the command most budget hosts hope you never run:
cat /proc/user_beancountersThis file reveals the truth. OpenVZ limits resources not just by RAM, but by obscure kernel parameters like numtcpsock (number of TCP sockets) or kmemsize. If you hit these limits, applications crash silently, even if you have "free RAM" displayed in your control panel.
The "Burst RAM" Myth
Many providers advertise "512MB RAM + 1GB Burst". This is marketing fluff. Burst RAM is essentially memory you can borrow if the node is empty. If another tenant on the node decides to compile a kernel or run a backup script, your Burst RAM vanishes instantly. The result? The OOM (Out of Memory) killer wakes up and terminates your MySQL process.
Security and Privacy in Norway
For our clients operating under Norwegian law (Personopplysningsloven), data integrity is non-negotiable. With OpenVZ, a vulnerability in the shared kernel can potentially expose all containers on the node. While patches are released quickly, the risk profile is higher than hardware virtualization.
Furthermore, iptables modules often need to be enabled on the host node. If you need complex firewall rules or VPN tunneling (TUN/TAP), you are often at the mercy of your provider's support ticket system.
The CoolVDS Approach: Reliability Over Density
At CoolVDS, we recognize that stability trumps density. While we offer OpenVZ for development and staging environments where cost is the primary driver, we configure our nodes differently:
- No Overselling: We hard-limit resources. If we sell you 1GB of RAM, that 1GB is reserved for you.
- I/O Fairness: We utilize CFQ (Completely Fair Queuing) schedulers on our storage arrays to ensure one heavy user cannot starve the disk I/O for others.
- Network Priority: With our datacenter located in Oslo, we guarantee low latency to the NIX (Norwegian Internet Exchange), but we also shape traffic at the veth interface to prevent UDP floods from affecting neighbors.
Pro Tip: If you are running a high-traffic Joomla or Magento store, stop looking at OpenVZ. You need the I/O isolation of Xen or KVM. The database contention on a shared kernel will eventually kill your response times.
Summary: When to Choose What
| Feature | OpenVZ Container | CoolVDS Xen/KVM |
|---|---|---|
| Performance | Fast, but inconsistent | Consistent, Guaranteed |
| Kernel Modules | Restricted | Full Control |
| Price | Low | Medium/High |
| Best For | DNS, Mail, Dev, Static Web | Databases, High-Traffic, eCommerce |
Don't let a shared kernel be the bottleneck for your business. Whether you need the raw efficiency of a container or the iron-clad isolation of a dedicated slice, ensure your provider understands the technology stack below the OS.
Need stable hosting with guaranteed resources? Deploy a high-performance instance on CoolVDS today and experience the difference of premium RAID-10 storage and unmetered gigabit connections.