I am putting a new server in a datacenter for company use and my company website. I use a lot of VPS accounts and in that world the choices are xen or openvz. I will be using virtualization on my dedicated server. It is difficult to find any information comparing the platforms outside of the VPS service context. We will not be renting out VPS accounts, we only wish to run isolated environments, and avoid the cost of multiple servers. I understand the basic difference of os level virtualization vs. hypervisor paravirtualization. It seems that most big companies are using xen, but in my experience openvz can achive better performance, due to the pooled resources, as many containers are likely to be idle. Does anyone have any experience with openvz or xen in this context?
Are there any other people than people who have access to the host using the VPS?
If yes: Xen else: openvz
One of the reasons for this is that you might end up rebooting a server. Unfortunately in OpenVZ this command doesn't work and results in a shut down server that needs to be booted from the host. Also have a look at LXC, it's the same as OpenVZ but doesn't use an as heavily patched kernel.
My personal favorite is still XEN. We decided to use it in 2007, since it was the best of breed back then with regards to performance and resource (CPU-overhead) usage.
We are using it with Linux in Dom0 and (mostly) Linux in PV-mode as DomUs.
If you need to run different Kernel Versions or different Linux distributions XEN is better - since you have the full Kernel in your VM.
If going for XEN have a look at Oracle VM, SLES11 SP2 or Citrix. It depends on your licensing needs which is the most cost-effective solution for you.
If you are in a pure Linux environment, KVM might be another possible solution nowadays (available in Debian, Ubuntu LTS, RedHat, SLES, ...).
See it for yourself: http://openvz.org/Performance
Executive summary: for pure computational cases there is no or little difference. For any other task the difference can be up to few times (in OpenVZ favor).