When you’re looking for a quality open source VPS, Xen and OpenVZ are two of the most popular and readily-available options. I’m going to take a look specifically at Xen, with periodic references to OpenVZ for comparison purposes. Following are a few pros and cons of Xen.
Pros:
1.   Swap Space
Though the swap space of a Xen configuration cuts slightly into your storage room, the advantage of the swap space is that you avoid crashes. Compare this to OpenVZ, and you see the capacity for crashes. As a NASCAR fan, I prefer OpenVZ. I even like it when my servers catch fire.
Keep in mind, burst memory is generally available for OpenVZ-configured servers, so that additional memory is available to users for limited periods of time. But burst memory does not create the same protection against crashes due to memory guarantees for each container (OpenVZ is OS-level or container-based virtualization vs. the paravirtualization of Xen).
2.   Kernel Liberty
Xen is equipped for loadable kernel modules and custom kernels. OpenVZ is not. However, OpenVZ’s one-kernel capacity typically makes system administration simpler. Obviously, though, Xen allows for a more diverse environment regarding kernels – it is the Indian corn of VPS’s.
3.   Compatibility with cPanel & WHM
If you are used to using cPanel & WHM, or if you just want to simplify your management of servers and sites, you can buy a license for usage with Xen servers. Note that this is also true of OpenVZ.
Cons:
1.   Density
Xen is not incredibly intuitive. You need to have expert knowledge of system administration and technical jargon. Diving into Xen cold can quickly become a nightmare – just like going to bed unarmed with Lindsay Lohan.
2.   Performance
Performance for systems using a Xen VPS can suffer due to its ability to customize one’s own kernel. Additionally, because of the swap space – which does have its advantages in terms of avoiding crashes – you can run into problems with VM’s grabbing all the swap space at the expense of the performance of other VM’s.
3.   Cost
Xen will probably be more expensive to run than OpenVZ. Yes, it’s robust and complex, and it’s customizable. The trade-off is that you will require a higher-end hosting package than you would for OpenVZ. Get out daddy’s wallet. Time to steal some more of our inheritance.
Conclusion
The gist is, different strokes for different folks. As you can see, OpenVZ and Xen have several distinct differences.
Do you have any thoughts on either system?
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by Kent Roberts and Richard Norwood
Sources:
1 http://www.vpslink.com/xen-vps/
2 http://thelinuxfix.com/blog/2011/10/27/openvz-vs-xen-some-vps-basics/
3 http://www.dedoimedo.com/computers/xen-intro.html