[Conan]

in Xen and KVM the RAM dedicated to you is pre-allocated and can't be used in other VMs.

Let's say the host node has 32GB ram.
You can fit 15 2GB VMs in it. Why 15? (15 x 2 is 30) You still need to leave RAM to use for the Operating System.

So technically, you can't oversell KVM / Xen Machines.


Unlike OpenVZ where anything isnt dedicated to you so it's prone to overselling. (Reason why OpenVZ is cheaper because they can create "unlimited" 2GB "VMs" on the host node)

[Dudi]

@Conan

I found a very good Xen vs. OpenVZ comparison: performance, which is a better VPS.



They wrote that in some cases OpenVZ has better performance than Xen or KVM, because its lower overhead, it needs less resources for background operation of the VPS.

https://www.solvps.com/blog/xen-vs-openv...rformance/

[Conan]

@Conan

I found a very good Xen vs. OpenVZ comparison: performance, which is a better VPS.



They wrote that in some cases OpenVZ has better performance than Xen or KVM, because its lower overhead, it needs less resources for background operation of the VPS.

https://www.solvps.com/blog/xen-vs-openv...rformance/

I do know about the performance between them.

OpenVZ is container based virtualization.
Xen/KVM/VMware/Virtualbox is hardware based since you virtualize even the hardware.

It's kinda obvious that OpenVZ can be faster than Xen and KVM on the right environment. Try doing it on your own dedicated server to find out.

[Sagnik]

OpenVZ IS faster but it is a bit of inferior quality...KVM is better than OpenVZ and its main advantage it that it does not allow overselling...Also if the provider oversells in OpenVZ and all users are using all the resources of their VPS, then there will be a performance degradation...But the BEST is VMWare but it is costly main due to licensing it...

[RickB]

I like KVM more. Run whatever OS you want, well OpenVZ supports plenty of Linux distros. Another con of OpenVZ is the old kernel OpenVZ is forced to use. However most of the time OpenVZ servers are cheaper. If you don't give a lot about security and you don't mind the higher risk of a slow CPU caused by possible abusers on your node and don't want to spend a lot of money on a server with relatively high specs, just go with OpenVZ!

[corrida]

Xen seems to be pretty good, it has multiple choice of OS, which is common, don't get me wrong. but I guess for OpenVZ, the prices and the speed really do put a "Number" into your hearts when you're purchasing it. So I would understand people buying the OpenVZ rather than most other ones. Also, the up-time for OpenVZ is 99.9%, which is nice =)

[SnoOpy]

In Closing we feel that a Xen VPS is the platform you should seek out if you are a looking to upgrade from shared hosting or need a server on the internet.
KVM is still to complex and OpenVZ…well, out of date.

[xdude]

Also if you are going to use Windows Server templates then you need KVM.

[RickB]

Also if you are going to use Windows Server templates then you need KVM.

Nope. You can also run Windows on VMWare and Xen.

[Unixfy]

As many others have pointed out already, the question can not really be answered. It depends on what you want to do.
If you just need process sepperation you should go with a container system like OpenVZ or any other, it is lighter you can (para)virtualize much more on the same hardware. It does not run its own kernel, it is basically just something like a jail for processes.
KVM on the other hand is different, it more or less simulates your own PC or Server inside your Sever, it runs it's on kernel which gives you the opportunity to install a totally different Operating System at the cost of resources.
It is like comparing a bike with a truck, more or less.
So it depends on your usecase, just want to run a webserver sepperated from your other applications, go with a container setup. Need to run another Operating System you have to go with full virtualisation.

Also older processors do not support full virtualisation at the cpu level, so your virtual machines will be slow, the only sensible thing there is to do a container setup.

No, OpenVZ is just an advanced chroot
It's not any lighter, it's just that resources are not dedicated so you can oversell. 
KVM doesn't technically run it's own kernel, it's just full virtualization not partial virtualization.

By the way, have you ever tried an OpenVZ container in a KVM VPS? It works