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Red Hat Pledges 'Integrated Virtualization'
OSS_ilation writes "Red Hat was all about virtualization in a recent announcement for an 'integrated virtualization' initiative with XenSource and chipmakers AMD and Intel. The move was seen as a way for Red Hat to bring its commitment to virtualization technology into 'sharper focus [...] with the release of a product roadmap that includes virtualization technology built into its enterprise version of Linux.' Red Hat's CTO, Brian Stevens, said the move would remove the complex 'rocket science' aspect of virtualization, and drive the technology into more enterprises as a result."
From what I gathered from the article, it looks like Red Hat is porting their distro to the Xen virtual machines and then packaging that with the natively-compiled OS as a virtual machine manager. It's nice to see a distro pick up Xen officially and package it an easy-to-use way, since Xen has very impressive performance. The article or the summary probably should have included a link to the Xen web site, so if you want to know more: the Xen site.
Systemd: the PulseAudio of init systems
Refer http://www.cl.cam.ac.uk/Research/SRG/netos/xen/ or http://en.wikipedia.org/wiki/Xen_(virtual_machine_ monitor).
/. bug #926803 - Why I can post.
It can take a couple of forms. In one form, it would be hooks for a VMM requiring a host OS.
In another form (which I know that Xen supports) it provides ways for the VMM to have control over the host OS, though Xen supposedly supports a number of these methods though ways not requiring modification to the source code.
There are others too (IE, replicating an image of a running OS, snapshotting the OS).
The article doesn't really tell you what they mean at all. I've seen all of these discussed in the context of Linux and Xen before. In fact, I thought that most of those were implemented.
A couple of months ago I was faced with the problem of needing to host multiple domains on one system. I initially considered Xen for my virtual servers need. However when I learned that this solution would not share the memory (each Vserver would have to have its dedicated memory) I decided to try out Linux Vserver. I have been a happy user of Linux Vserver since then.
With Linux Vserver you only run one kernel on your system where with Xen each virtual server runs its own kernel. This presents some limitations for Linux Vserver. For example the guest virtual servers cannot have the network loopback interface lo. But almost all of these I could live without.
Now if I want to start adding more virtual servers I can, without having to worry about running out of memory.
To put it simply (I don't know the more in-depth stuff off the top of my head) Xen won't run an unmodified x86 OS as a guest (DomU). Instead of actually emulating the physical devices it provides ways for the guest OSes to request services from it through specialized "drivers", for one thing. Once the kernel/driver work is done, however, the fact that you're running under Xen does not affect your userspace apps.
So you can only run operating systems that have been modified to run under Xen. So far Linux, FreeBSD, NetBSD and Plan9 have undergone modification, at least according to http://wiki.xensource.com/xenwiki/OSCompatibility
Only the technology is named User Mode Linux (UML) instead of Xen. Xen still requires you to jump trough quite a number of hoops before you have a virtual machine running. With UML it is so simple you can start, stop & create new ones on demand like is done at linuxzoo.net
With xen you need a modified host kernel and do some tricky stuff with LVM to use Copy on write disks. With lvm it is the default, you can just point to a base image and have the users modifications in a separate file. The downside is the speed penalty: UML is 40-50% slower than Xen.
This space is intentionally staring blankly at you
This is no longer true with the use of Intel's VT or AMD's Pacifica CPU features. Xen originally had to have this OS-level hack because of limitations of the x86 architecture making it impossible to completely virtualize. Intel and AMD have solved this. You can buy Pentium 4's with VT *right now* and run un-modified windows guest's on Xen. The AMD M2 and the next set of Intel chips (the core/core-duo's desktop and server cousins) will all support this.