Virtuozzo vs Xen
Virtuozzo and Xen are virtualization solutions that allow running multiple virtual environments within a single machine. These solutions are popular among VPS providers and are the two most popular solutions for Linux VPS providers. Most of the differences between Virtuozzo and Xen arise from the fact that Virtuozzo use OS-level virtualization, whereas Xen use paravirtualization.
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[edit] Virtualization Technology
Virtuozzo uses OS-level virtualization, meaning that the environment inside a VM is basically like a chroot. The kernel is shared between VMs on the same machine. This means that all VMs are using one single kernel, which takes care about proper isolation and resource management for all the VMs, such as memory limiting, CPU and IO scheduling. Virtuozzo VMs use the same file system (i.e. VM root is just a directory on the host, no need to have a special partition), so the host has simple and open access to the guests' files (which is helpful in VM backup and recovery scenarios).
Xen uses paravirtualization, which is similar to the technology VMWare uses to virtualize its VMs [Not strictly true, VMWare takes a full-virtualisation - hardware emulation approach]. VMs running under Xen behave as if they are running on a dedicated box, so each Xen guest runs its own kernel, can load kernel modules etc.. The VM is given virtual hardware to run its environment, and therefore, resource statistics look as if the VM is running on a dedicated box.
Both solutions have their pros and cons. Xen is great for running different operating systems, while Virtuozzo provides better density and performance.
[edit] Supported Platforms
Virtuozzo allows both Windows and Linux guests (on a different servers). Xen works with Linux guests on all hardware but for Windows it's need hardware virtualization support in CPU level AMD-V and Intel VT.
[edit] Performance
HP labs has published a performance comparison of Xen and OpenVZ (an open source version of Virtuozzo): http://www.hpl.hp.com/techreports/2007/HPL-2007-59R1.pdf
According to their findings:
- For all the configuration and workloads we have tested, Xen incurs higher virtualization overhead than OpenVZ does
- For all the cases tested, the virtualization overhead observed in OpenVZ is limited, and can be neglected in many scenarios
- OpenVZ density is at least 50% higher than that of Xen (Xen systems becomes overloaded when hosting four instances of RUBiS, while the OpenVZ system should be able to host at least six without being overloaded)
[edit] License
Virtuozzo is proprietary software and must be licensed per VM. Xen is open-source and is free to use by anybody.
There is an open-source version of Virtuozzo called OpenVZ that is limited to the command line and misses the Virtuozzo's GUI and Web-based control panels.
