Virtual Private Server Comparison

Virtual Private Servers are now fairly common on the Linux web hosting scene. One of the most popular VPS technologies is offered by hosting companies is Virtuozzo produced and developed by SW-Soft. There are "free" or open source alternatives available which are worthy of consideration. The technology offered by the Xen Hypervisor Engine is particularly exciting enabling commodity server hardware based on the AMD or Intel platform, to be partitioned into smaller virtual or private servers. Some of the later Linux distributions such as Fedora Core 4 have support for Xen Virtualisation. The additonal overhead of running a Xen Virtual Dedicated Server is typically very low. This makes it potentially more efficient than the excellent User Mode Linux (UML) which has proven itself well in the virtual hosting field. UML uses emulated system calls and disk drivers which make it slower, when it comes to context switches and disk I/O. Xen is a "hypervisor" with the host operating system a Virtual Machine (VM) under it. This makes for a very low overhead of typically 2-8%. Linux VServer is similar in principle to Virtuozzo though the implementation is quite different. However there are similarities in that VServer and Virtuozzo adopt a shared kernel with security isolation (a chrooted init) using context and capabilities to limit the power of the superuser within the VM. Though they may lack many of the features of a "true" virtual machine, such as no low level networking, and the ability to use or load certain kernel modules (for instance Xen allows you to maintain the virtual machine as if it were a real hardware device, using the common and well known up dating tools such as apt-get and yum) however these are not likely to be important to the average hosting customer who is more likely to choose a solution which is totally managed by his ISP. Another advantage to a Hosting ISP is that with Virtuozzo the file system is quota based which allows for a slight "overselling" of web space if most of the customers don't use all their disc space. In a way this is similar to normal "virtual hosting." Additionally the virtuozzo vps customer who is on a "quiet" hardware node will enjoy the full resources of the server! Despite Virtuozzo having some hardware limitations, in the hosting market which it was designed for, this is not considered relevant. However SW-Soft are widening support and compiling additional modules into the Virtuozzo kernel, indeed Virtuozzo is now available for AMD processors. Additionally Virtuozzo possesses an operating system templating system, with a cache so that popular software can be shared by multiple vps's on a hardware node and they can all be patched and updated at the same time. We are asked if a Virtual Machine with just 32MB or 64MB of RAM is actually useful for anything, but with Linux the memory is used efficiently so for testing software under different operating systems, hosting a few mainly static websites, or for use as a root shell account on a well performing network (for perhaps training purposes) they are ideal. We have put Xen Virtual Dedicated Servers to use in the following applications: * Web Server * Mail Server * DNS Server * Mail or DNS secondary * Development Box * An RPM build environment * Nagios Network Monitoring Node * Shell Account Hosting * An advanced reseller solution (with Control Panel) In an interesting and welcome move, SW-Soft have opened up and "open sourced" a subset of Virtuozzo in the form of OpenVZ. Not all the Virtuozzo management utilities are there , but OpenVZ while bleeding edge than the commercial version is stable and usable as well as supporting templated versions of 2.6* kernel based distributions such as FC4. -Paul Lee