The OpenVZ Illusion: Why "Burst RAM" Is Killing Your Uptime
It is 3:00 AM in Oslo. Your monitoring system just SMS'd you: the database is down. Again. You SSH in, restart mysqld, and everything seems fine. No logs, no errors in /var/log/messages. Just a silent death.
If you are running on a budget VPS provider using OpenVZ, you are likely the victim of the "Burst RAM" lie. As a systems architect dealing with high-traffic LAMP stacks across the Nordics, I see this scenario every week. The hosting provider sells you "512MB RAM + 1GB Burst," but the moment you actually try to use that burst, the kernel OOM (Out of Memory) killer steps in—or worse, the container simply refuses to allocate memory without logging a standard error.
In this post, we are going to look under the hood of OpenVZ, analyze the dreaded user_beancounters file, and explain why serious production environments in 2009 demand true hardware virtualization like Xen or the emerging KVM standard found on CoolVDS platforms.
The Architecture: Containers vs. Hypervisors
To understand the problem, you have to understand the kernel. OpenVZ is operating system-level virtualization. There is one single Linux kernel (usually a patched Red Hat 2.6.18 kernel) running on the host node. Your "server" is just a chrooted environment with some resource limits applied.
In contrast, technologies like Xen (Paravirtualization) or KVM (Kernel-based Virtual Machine) provide a distinct kernel for each user. This isolation is critical. In OpenVZ, if a neighbor on your node launches a fork bomb or a heavy I/O task, your load average spikes even if your CPU is idle.
Pro Tip: Rununame -rinside your VPS. If you see something containing "stab" or "openvz", you are sharing a kernel. If you cannot load kernel modules likeiptables_natwithout asking support, you are in a container.
The dirty secret: /proc/user_beancounters
Most sysadmins know free -m. On OpenVZ, that command is a liar. It shows you what the host wants you to see. The truth lies in a specific file that governs your container's existence.
Run this command right now:
cat /proc/user_beancounters
You will see a table with columns like held, maxheld, barrier, limit, and the most frightening one: failcnt.
| Parameter | Description | The Danger |
|---|---|---|
| privvmpages | Memory allocation limit. | If held hits limit, applications crash (malloc fails). This is usually where MySQL dies. |
| kmemsize | Kernel memory size. | Even if you have RAM free, hitting this limit prevents new processes from starting. |
| numproc | Max processes. | Apache spawning too many workers? Fork failure. |
If the failcnt column is anything other than 0, your applications are being silently throttled or killed. This is why we argue that for anything beyond a simple DNS server or a dev sandbox, OpenVZ is a liability.
The "Noisy Neighbor" and I/O Latency
Here in Norway, we pride ourselves on infrastructure stability. But even if your data center in Oslo has redundant power, your server stability relies on disk I/O. OpenVZ schedulers often do a poor job of isolating I/O wait.
I recently audited a Magento installation for a client. Their site was crawling during peak hours. The CPU usage was low, but iostat showed massive wait times. It turned out another customer on the same physical node was running a massive backup script, thrashing the SATA disks. Because OpenVZ file systems are shared directories on the host, there was no true I/O partitioning.
The Solution: True Isolation
This is where the industry is heading. Technologies like Xen and KVM allocate dedicated blocks of RAM and offer far stricter I/O scheduling. When you buy 512MB RAM on a CoolVDS Xen instance, that memory is reserved for you at the hypervisor level. It cannot be "burst" into by a neighbor.
Furthermore, regarding storage performance—critical for databases—CoolVDS utilizes high-speed RAID-10 SAS arrays and is beginning to roll out enterprise-grade SSD caching (using Intel X25-E technology). This ensures that I/O bottlenecks are virtually eliminated.
Data Privacy: The Norwegian Context
We must also consider the legal landscape. With strict enforcement from Datatilsynet (The Norwegian Data Inspectorate) and the Personal Data Act (Personopplysningsloven), you need to know exactly where your data lives. In shared kernel environments, the barrier between your customer data and the host administrator is thinner than in hardware-virtualized environments.
For sensitive data, full virtualization adds a necessary layer of security, reducing the attack surface from kernel exploits that could potentially escalate from a container to the host.
Conclusion: Choose the Right Tool
OpenVZ isn't useless. It is fantastic for:
- Low-cost testing environments.
- VPN tunnels (if TUN/TAP is enabled).
- Static HTML sites with Nginx.
But if you are running a business-critical MySQL database, a Java application (Tomcat/JBoss), or an e-commerce store targeting the Norwegian market, you need guaranteed resources.
Don't let a privvmpages error cost you a customer. Upgrade to a platform that respects resource isolation.
Ready to stop fighting failcnt? Deploy a true KVM or Xen instance on CoolVDS today and experience the stability of dedicated resources.