OpenVZ Containers: The Efficiency Trap vs. Raw Performance

If I see one more hosting provider marketing a "2GB RAM VPS" that is actually just an OpenVZ container with a massive burst limit and zero guaranteed memory, I might just write a script to dd their disk arrays into oblivion. It is 2010. We are moving beyond shared hosting, but we are walking into a minefield of oversold virtualization.

In the Norwegian hosting market, latency to NIX (Norwegian Internet Exchange) is low, but that doesn't matter if your CPU is fighting for cycles because your neighbor on the physical node is compiling Gentoo. Today, we are tearing down the OpenVZ architecture, looking at /proc/user_beancounters, and deciding when to use containers and when to demand hardware virtualization like Xen.

The OpenVZ Reality: Thin Provisioning on Steroids

OpenVZ is operating system-level virtualization. It uses a single patched Linux kernel (usually RHEL 5 or CentOS 5 based) that handles all the guest instances (containers). There is no hypervisor emulation layer. The guests talk directly to the host kernel.

The Pro: It is fast. Near-native speeds. Sysbench CPU tests on OpenVZ often outperform Xen PV because there is no instruction translation overhead.

The Con: The "Noisy Neighbor" effect. Since there is no strict isolation of I/O or CPU scheduler (prior to recent VSwap improvements), one heavy user can degrade the performance of the entire node.

The "Burst RAM" Lie

The most dangerous setting in an OpenVZ config is the distinction between guarautied (Guaranteed) and privvmpages (Burst). Unscrupulous hosts sell you the Burst limit.

Pro Tip: Log into your VPS right now and run:

cat /proc/user_beancounters

Look at the failcnt column. If it is anything other than zero for privvmpages, your applications are silently being killed by the kernel because the host node is out of RAM, regardless of what your free -m command says.

When Architecture Breaks Compliance

Here in Norway, the Personopplysningsloven (Personal Data Act) places strict requirements on data integrity. With OpenVZ, if the host kernel panics, every single VPS on that node goes down. For a personal blog, that is fine. For a business hosting customer data in Oslo, that is a single point of failure you cannot afford.

Furthermore, tuning kernel parameters is a nightmare. Need to load a specific iptables module for your firewall or modify sysctl.conf for high-concurrency TCP connections? You often can't. You are locked into the host's kernel version.

The Xen Alternative (and why we use it)

At CoolVDS, while we respect the efficiency of OpenVZ for development sandboxes, our production-grade infrastructure relies heavily on Xen Hardware Virtualization (HVM) and Paravirtualization (PV).

Optimizing for 2010's Web

If you are running a LAMP stack (Linux, Apache, MySQL, PHP) on a VPS, disk I/O is usually your bottleneck. We are seeing a shift from standard SATA drives to 15k RPM SAS RAID-10 arrays in enterprise setups. Some pioneers are even testing early Intel X25-E SSDs for database journals, though the cost per GB is still astronomical.

If you must stay on OpenVZ for budget reasons, optimize your MySQL `my.cnf` to respect the `kmemsize` limits. Do not set your `innodb_buffer_pool_size` based on the burst RAM; set it based on the guaranteed RAM minus 20% for the OS overhead.

Conclusion: Choose Stability Over Marketing

Don't get dazzled by cheap offers promising "unlimited" resources. In the datacenter, physics still applies. If you need raw density, OpenVZ is a tool. If you need guaranteed performance and strict data separation required by Norwegian standards, you need hardware isolation.

We built the CoolVDS platform to solve the "failcnt" headache. Whether you choose our high-density containers or our dedicated Xen instances, you get transparency on what resources you actually own.

Is your current VPS swapping to disk? Run a test instance on CoolVDS today and experience the difference of uncrowded 15k SAS arrays.