Stop Letting 'Burstable RAM' Destroy Your Uptime

It’s 3:00 AM. Your monitoring system is screaming. Your Apache process is hung, but the load average is suspiciously low. You SSH in, run top, and everything looks fine—except your site is crawling. If you are hosting on a budget VPS, you are likely the victim of the 'noisy neighbor' effect, a classic symptom of oversold OpenVZ containers.

In the current hosting landscape of 2009, virtualization is the buzzword. But not all virtual private servers are created equal. As we build out infrastructure for clients from Oslo to Trondheim, we see too many developers getting burned by the nuances of Operating System-level virtualization (OpenVZ) versus Paravirtualization/Hardware Virtualization (Xen/KVM). Let’s look at the kernel-level reality.

The OpenVZ Trap: It's Not Really Your Server

OpenVZ is containerization. It creates multiple isolated execution environments (VEs) on a single Linux kernel. The host node runs one kernel, and you—along with 50 other customers—share it.

The Pros

• Density: It’s cheap. Hosts can pack hundreds of containers on one physical box.
• Instant Scaling: Changing resources can happen without a reboot (often).
• Native Performance: Since there is no hypervisor emulation layer, disk I/O and CPU execution are practically native speed—if the host isn't overloaded.

The Cons (The Dealbreakers)

The problem isn't the technology; it's the economics. OpenVZ allows hosts to oversell resources aggressively. They promise you 512MB RAM, but it's often 'Burstable' RAM, not dedicated.

The War Story: Last month, I audited a client's slow MySQL setup. They were on a cheap OpenVZ plan. I checked /proc/user_beancounters—the file where OpenVZ logs resource limits.

cat /proc/user_beancounters 
UID  resource           held    maxheld    barrier      limit    failcnt
...  privvmpages       45000      48000      50000      52000      4392

See that failcnt (failure count)? That number was climbing every second. The host machine was out of physical RAM, so the hypervisor was killing my client's MySQL threads to save the neighbors. No amount of my.cnf tuning solves that. You need dedicated physical RAM.

Xen: The Professional's Choice

At CoolVDS, we lean heavily towards Xen (and are experimenting with the promising KVM modules in the newer 2.6.20+ kernels). Xen provides stronger isolation. RAM is reserved at boot time. If you buy 1GB of RAM, that memory is allocated to your domain and no one else can touch it.

Furthermore, Xen allows you to load your own kernel modules. Need ip_conntrack for complex firewall rules? Need a specific TCP congestion control algorithm? On OpenVZ, you have to beg your host to enable it on the node. On Xen, you are root in the truest sense.

Data Integrity and Norwegian Law

We operate under the purview of the Personopplysningsloven (Personal Data Act). While Datatilsynet hasn't explicitly banned shared kernels, there is a security implication. In a shared kernel environment (OpenVZ), a vulnerability in the kernel affects every container. In a hardware virtualized environment (Xen), a kernel panic in your VM stays in your VM.

Pro Tip: Always check your disk scheduling. On a Xen VPS, the default scheduler might be set to `cfq`. For virtualized environments running on our high-speed RAID10 SAS arrays, switching to the `noop` scheduler often reduces CPU overhead because the physical RAID controller handles the sorting.
echo noop > /sys/block/xvda/queue/scheduler

The Verdict

If you are running a static dev site or a low-traffic blog, OpenVZ is cost-effective. But for production applications where latency matters—where you need stable I/O for databases and strict resource guarantees—you cannot rely on 'burst' resources.

We engineered CoolVDS to solve exactly this. We don't play the overselling game. Whether you choose our container solutions or our premium Xen instances, our resources are hard-capped and guaranteed. We utilize enterprise-grade 15k RPM SAS drives to ensure that even under heavy load, your I/O wait remains negligible.

Don't let a noisy neighbor kill your uptime. Deploy a VPS that actually respects your root privileges.