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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, QEmu also can do that, but those snapshots seem to be quite a bit bigger than the snapshots OpenVZ takes. I don't have an example at hand, but the difference was quite significant.

Overall I am pretty impressed by OpenVZ. I think that for pure server-virtualization it might be the way to go, as the overhead, as mentioned, really is minimal. I have two VMs (CentOS 4 and Fedora 7, both OpenVZ) running in a virtualized CentOS 5 (KVM) and if I SSH into them or enter them using vzctl I feel no difference compared the host (the CentOS 5 VM that is).

I'll keep playing with this. As some of you folks may have guessed from previous posts I really like virtualization, and as the folks from Symantec (yes, there was another Symantec-event, post follows shortly) just recently also mentioned (not that I wouldn't have known that already) it is a thing step on the way towards green IT.