The Truth About Virtualization: Why Xen PV Beats OpenVZ for Serious Workloads

Let’s be honest. The VPS market right now is a minefield of marketing fluff. If I see one more provider advertising "Burstable RAM" as if it's a feature rather than a liability, I might just `rm -rf /` my own workstation. In the world of hosting, there are two types of virtualization: those designed to pack as many customers as possible onto a single chassis (OpenVZ), and those designed to behave like actual servers (Xen).

At CoolVDS, we are tired of the overselling game. If you are running a high-traffic forum, a Magento shop, or a critical database, you cannot afford to have your CPU cycles stolen because a neighbor on the same node decided to compile a kernel. This is your complete guide to why we use Xen, how to tune it, and why hosting in Norway matters more than you think.

The Architecture of Isolation: Xen PV vs. The Rest

In 2010, the debate often lands on OpenVZ versus Xen. Here is the reality: OpenVZ shares the host kernel. It relies on user_beancounters to limit resources. It is lightweight, yes, but it allows providers to oversell memory aggressively. When the host node hits swap, your application dies.

Xen, specifically Xen Paravirtualization (PV), is different. It uses a hypervisor layer that sits directly on the hardware. Your VPS (domU) runs its own kernel. It talks to the hypervisor, which talks to the hardware. This isolation is non-negotiable for performance consistency.

Pro Tip: To check if your current provider is stuffing you into an OpenVZ container, check your kernel release. Run uname -r. If you see "stab" or "vig" in the string, or if you cannot load your own kernel modules (like iptables specific modules), you are in a container. Time to migrate.

Tuning for Performance: Beyond the Default Install

Just provisioning a Xen VPS isn't enough. You need to tune the guest OS to respect the virtualized environment. Here is a configuration we often apply to high-load database servers running on CentOS 5 or Debian Lenny.

1. The I/O Scheduler

By default, Linux uses the CFQ (Completely Fair Queuing) scheduler. On a physical spinner, this is fine. On a Xen domU, the hypervisor (dom0) handles the physical disk ordering. Your guest OS trying to re-order requests is just wasting CPU cycles.

Switch your scheduler to noop or deadline. In your /boot/grub/menu.lst, append this to your kernel line:

This passes I/O requests directly to the hypervisor without complex reordering logic, reducing latency significantly.

2. Swap and Memory Management

Xen handles memory strictly. If you are allocated 512MB, you get 512MB. However, Linux loves to swap things out to be "safe." On a VPS, disk I/O is the most expensive resource. We want to avoid swapping at all costs.

Edit /etc/sysctl.conf to lower your swappiness:

vm.swappiness = 10
# Default is usually 60, which is too aggressive for a VPS

Apply it with sysctl -p. This forces the kernel to use every bit of physical RAM before touching the disk.

The Storage Bottleneck: Why RAID-10 is Mandatory

We are starting to see the first generation of Enterprise SSDs hit the market, specifically the Intel X25 series. While they offer incredible IOPS, the price per gigabyte is still astronomical for general hosting. Until SSDs become standard (give it a few years), the gold standard remains 15k RPM SAS drives in RAID-10.

Why RAID-10? It strips data across mirrored pairs. You get the speed of striping (RAID 0) with the redundancy of mirroring (RAID 1). RAID 5 or 6 requires parity calculations, which kill write performance. If your host uses RAID 5 for VPS storage, they are prioritizing their storage density over your database performance.

At CoolVDS, we don't gamble with parity. We use hardware RAID-10 with battery-backed cache units (BBU). This ensures that even if power flickers, the write cache is preserved.

The Norwegian Advantage: Latency and Legality

For our clients in Scandinavia, geography is physics. Hosting in Germany or the US adds milliseconds that accumulate. Pinging a server in Oslo from Bergen takes roughly 10-15ms. Pinging Texas takes 130ms+. For a static site, this is negligible. For a dynamic application involving many database queries per page load, that latency compounds.

Data Protection in 2010

We also need to talk about compliance. The Norwegian Personal Data Act (Personopplysningsloven) places strict requirements on how personal data is handled. While the US Safe Harbor framework exists, many Norwegian businesses prefer—or are legally required by Datatilsynet—to keep sensitive data within national borders.

By hosting on CoolVDS servers physically located in Oslo, you are directly peering at NIX (Norwegian Internet Exchange). Your traffic stays local, and your data remains under Norwegian jurisdiction. It is a clean, legally sound architecture.

The CoolVDS Standard

We don't sell "burstable" limits because we don't believe in overselling. When you buy a slice of our Xen infrastructure, those resources are reserved for you.

• Virtualization: Xen PV (or HVM for Windows)
• Storage: Enterprise SAS 15k RAID-10 (High-speed I/O)
• Network: Gigabit uplink to NIX
• OS Support: Ubuntu 10.04 LTS, CentOS 5.5, Debian 5

Don't let your project fail because your host decided to cram 500 containers onto one server. Real systems architecture requires real isolation.

Ready to test the difference? Deploy a Xen instance on CoolVDS today and see what uptime really looks like.