Stop Sharing Your Kernel: The Definitive Guide to Xen Virtualization
Let’s be honest. If I hear one more hosting provider claim their $10/month VPS offers "dedicated resources" while running Virtuozzo or OpenVZ, I might just pull the plug on the rack myself.
Here is the ugly truth of the hosting market in 2009: Most "Virtual Private Servers" are just glorified chroot environments. You are sharing the kernel, the I/O scheduler, and often the memory limits with a hundred other users. When User A decides to compile a massive kernel or run a fork bomb, your MySQL process gets killed by the OOM (Out of Memory) killer. I've seen it happen on production servers from Kyiv to Oslo.
For serious systems architects, the answer isn't shared hosting. It's Xen.
The Architecture of Isolation: Paravirtualization (PV)
Unlike full virtualization (which is still heavy on overhead, though KVM is looking interesting in the latest Linux kernels), Xen uses Paravirtualization (PV). This allows the guest OS (domU) to talk directly to the hypervisor API. It knows it's virtualized, and it cooperates.
Why does this matter for your business in Norway? Predictability.
When you deploy a LAMP stack on a Xen node, you get a hard allocation of RAM. It’s not "burstable" RAM that vanishes when the host is busy. It is reserved for you. This is why we built the CoolVDS infrastructure strictly on Xen.
Identifying Your Environment
Not sure what you are currently running? Check your kernel. If you see 2.6.18-028stab064, you are likely inside an OpenVZ container (the "stab" gives it away). In Xen, it looks different.
# uname -r
2.6.18-164.el5xen
If you have access to /proc/user_beancounters, you are definitely not on a true VDS. You are in a container. Get out.
Performance Tuning: The 2009 Sysadmin Standard
Just getting a Xen VDS isn't enough. You need to tune it. The default CentOS 5.3 install is designed for compatibility, not speed.
1. Disk I/O Scheduler
The default scheduler is usually CFQ (Completely Fair Queuing). In a virtualized environment, the host (dom0) handles the physical disk sorting. Your guest shouldn't waste cycles re-sorting requests.
Switch your elevator to deadline or noop for immediate throughput gains.
# echo noop > /sys/block/xvda/queue/scheduler
To make it permanent, add elevator=noop to your kernel line in /boot/grub/menu.lst.
2. The Swap Trap
On Xen, disk I/O is expensive compared to RAM. You want to avoid swapping at all costs. Adjust your swappiness in /etc/sysctl.conf:
vm.swappiness = 10
This tells the Linux kernel to prefer dropping filesystem caches over swapping out application memory. For a database server running MySQL 5.0 or 5.1, this is critical.
Pro Tip: If you are running high-traffic sites, don't rely on the default ApachepreforkMPM. Switch toworkerMPM or, if you're feeling adventurous, put Nginx 0.7 in front as a reverse proxy. It handles static files with a fraction of the RAM Apache needs.
Data Sovereignty and Latency
Latency matters. If your customer base is in Scandinavia, hosting in Texas is a mistake. The speed of light is a hard limit. A packet round-trip from Oslo to Dallas is ~130ms. From Oslo to a local datacenter? <5ms.
Furthermore, we have to talk about the Personal Data Act (Personopplysningsloven) and the role of Datatilsynet. Keeping your data within Norwegian borders (or at least the EEA) simplifies compliance massively compared to navigating the US Safe Harbor framework.
| Feature | Budget VPS (OpenVZ) | CoolVDS (Xen PV) |
|---|---|---|
| Kernel | Shared (Risky) | Isolated (Stable) |
| RAM Allocation | Burstable / Oversold | Dedicated / Reserved |
| Storage | Shared Filesystem | LVM / Block Device |
| Swap | Often Unavailable | Full Control |
Why We Choose RAID-10 SAS Over SATA
At CoolVDS, we often get asked why we don't use massive 1TB SATA drives. The answer is IOPS (Input/Output Operations Per Second). A 7.2k RPM SATA drive pushes maybe 80 IOPS. A 15k RPM SAS drive pushes 180+.
When you put four SAS drives in RAID-10, you get redundancy AND speed. Until Solid State Drives (SSDs) become affordable for enterprise mass storage (maybe in a few years?), 15k SAS is the gold standard for database hosting.
The Verdict
Virtualization is about simulating hardware, not just isolating processes. Xen gives you that hardware simulation. It allows you to run your own kernel modules, configure your own iptables without restrictions, and guarantees that your RAM is actually there when you need it.
Don't let a noisy neighbor kill your uptime. Experience the stability of true hardware isolation.
Ready to compile your own kernel? Deploy a Xen instance on CoolVDS today and get direct connectivity to NIX (Norwegian Internet Exchange).