Sunday, April 23
It's an open source subset of Virtuozzo, which is a virtualising system aimed primarily at hosting providers. Mughi, the latest addition to the mu.nu family, is a virtual server running under Virtuozzo.
The neat thing about OpenVZ (and Virtuozzo) is what it isn't: It isn't a complete system-level virtualisation. It's a user-level virtualisation. Under OpenVZ, you have one Linux kernel for the entire (physical) system. Under something like VMWare, you have a separate kernel for each virtual machine. The VMWare way gives you complete isolation (good), but it means that each virtual server ends up trying to manage its own disk caching and virtual memory (wasteful). With OpenVZ, you have a single caching and virtual memory pool, but you can restrict how much memory (and also CPU time) a single virtual machine can take up. This does mean that I can see how much physical memory the server has (8GB, of which 256MB is guaranteed to Mughi), but for many purposes that matters less than the efficiency gained by the sharing of that memory.
There's a 119 page PDF manual available if you want to know more.
It is only supported on certain specific versions of Linux (the manual lists Fedora Core 3 and 4, and Red Hat Enterprise 4), but you can run other distributions inside the virtual machines; it's only the kernel that must be shared. (It looks like CentOS, Fedora 5, and SUSE 10 are now supported as well.)
Ooh. And they also have checkpointing and virtual server migration, which is pretty neat for free software.
And then there's Xen. I really need to read up on that too.
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