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Virtual once more: OpenVZ

At work we got ourselves a virtual server now.
And looking around I found out that it uses Virtuozzo, a solution I didn't get around to look at yet.

Yes, I have read about it before, and I know that there is a free implementation called OpenVZ, and I've even been on their site already, but still I didn't get around to try.

So now we got that server, and that finally made me try...

Unlike QEmu (Full Virtualization) or Xen (Paravirtualization) Virtuozzo and OpenVZ use OS Level Virtualization, which seems to be quite similar to the branded zones available in Solaris.

This kind of virtualization is pretty interesting as it involves a very low overhead, and seems to scale really well. The reason probably is that this solution doesn't emulate a full system but only puts stuff into container, somehow comparable to a chroot-environment, but more flexible since it also is possible to run other distributions, but not other OSs (like for example Windows), in it.

So, what I did now is setting up a virtual machine (in KVM) with CentOS 5 (as integration for OpenVZ seems to work best with RedHat-systems). As I have the 5.1 DVD I first upgraded the system to the current 5.2 and then installed the OpenVZ-kernel, tools and templates.

Templates describe what the virtual system is made from, packages and stuff like that. ;-)
I installed the templates for CentOS 4 and Fedora 7 and created VMs with those.
All pretty easy and doesn't take too long (packages are just downloaded once and then cached for later use).

What's really nice, compared to other solutions, is that the files are not in a container-file, but just within the file-system. That makes it a lot more flexible in terms of assigning disk-space to the virtual-machine.
Also it makes it easy to install and upgrade packages, this can easily be done, along with other management-tasks, without even entering the VM.

Scripted management of multiple machines thus easily is possible.

Another nice feature is creating snapshots. Okay, Q