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[luke_a]

Linux Kernel Virtual Machine (KVM) vs Xen

I am currently researching the options open to me for Virtualisation, the two main ones I have seen are Xen or KVM.
I mainly use CentOS (RHEL), but have read that the version of Xen with it is very old, broken and unstable. KVM isn't included in the kernel that ships with CentOS, as it is too old, apparently it was first featured in Kernel v2.6.20. There isn't likely to be an update till RHEL6, which is due for release first quarter of 2010. I can't wait over a year, so need to find another Distro for use as the Host OS/Hypervisor.
I have built a pretty powerful server, it has an Intel Xeon 3230 which has VT - so I might be better off using KVM over Xen. I am going to collocate this server, so realistically I can make this decision only once - as it would be a PITA to re-install a host Linux distro remotely.
I did a search on distrowatch for distros with the latest version of the kernel, and Slackware came up as being just one minor version behind the most current (v2.6.27.7). Now this distro is very mature, so should be a fairly safe bet, but it is a 32bit version and can't host 64bit VMs. I have 8GB of ram so want to be able to use it all, and offer the choice of 32/64bit VMs. So that's that out of the window.
I have used Arch Linux on and off for a couple of years as a workstation OS, but because it is so bleeding edge, when pacman updates it can break itself. But I suppose if I just use it as the Host OS, and never let it update/reboot, then it won't break. It should be fairly lightweight and stable, as I will be installing the bare minimum packages. I have a management card, so if the server fails to boot, then I can still remote in to fix it. If I do want to update the kernel, is it possible to update without rebooting? I think it is somehow... unless I can just reboot during an unused time at 3am or something.
As you can tell I am leaning towards KVM on Arch Linux (x86_64). Is this a good plan?

[Adam-AEC]

I have a few nodes that run CentOS5 with Xen.
I've updated to Xen3.3 using some pre-built RPMs. This was required for a newer version of libvirt. You'll need to rebuild the ramdisk to include the xen modules if you install from the repo. I documented the procedure if you choose to go this route and need to see how it's done.
Even though Ubuntu is talking about switching from Xen to KVM, the latest release (Intrepid?) has a fairly recent Xen kernel, iirc. You could consider Ubuntu Server too.





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[PCS-Chris]

Quote:



Originally Posted by luke_a


I am currently researching the options open to me for Virtualisation, the two main ones I have seen are Xen or KVM.
I mainly use CentOS (RHEL), but have read that the version of Xen with it is very old, broken and unstable....


The Xen provided with CentOS 5 is not old or broken. The focus of CentOS is stability. Therefore it sticks with a certain version of a package through the life of the OS, just providing patches and ongoing support for bugs and security fixes.
The default Xen in CentOS is also backported and I think you will find is MUCH more stable than the latest and greatest version of open-source xen over at www.xen.org. Unless you are wanting reasonable performance from Windows VM's on Xen I would stick with the proven, stable version of Xen (3.1 + many many fixes etc) shipped with CentOS rather than going for the latest and greatest builds which are (from experience) full of bugs.





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[Dave - Just199]

Or you could just load up openvz and be done with this whole thing.





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[Mike - Limestone]

Quote:



Originally Posted by keepr


Or you could just load up openvz and be done with this whole thing.


Another nod for OpenVZ here. I'm not sure the OP's particular needs, but OpenVZ is excellent in most situations.
-mike





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[zaitcev]

Quote:



Originally Posted by luke_a


I mainly use CentOS (RHEL), but have read that the version of Xen with it is very old, broken and unstable.


Says who?
Quote:



Originally Posted by luke_a


I did a search on distrowatch for distros with the latest version of the kernel, and Slackware came up as being just one minor version behind the most current (v2.6.27.7).


If you're desperate enough to consider Slack, you need to take a good breath and reassess your options. Why don't you install Fedora 10 as a host, for example?
I run F9 as the host system with OpenVZ and it drives CentOS 5 clients just fine. Sadly, I don't have a direct exposure to KVM.
If I wanted wildly disparate hosts and guests NOW and OpenVZ would be excluded, I would use Xen with F9. Keep in mind, it should be possible to retain Xen clients and switch to KVM hypervisor by using Xenner in the future.

[PCS-Chris]

FYI Fedora 10 does not include host (Dom0) support.





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[Adam-AEC]

Quote:



Originally Posted by PCS-Chris


FYI Fedora 10 does not include host (Dom0) support.


Neither does Ubuntu 8.10 :\





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[luke_a]

Quote:



Originally Posted by zaitcev


Says who?


I posted another thread about Xen awhile ago, and someone responded saying it was broken on CentOS.
Quote:



Originally Posted by zaitcev


If you're desperate enough to consider Slack, you need to take a good breath and reassess your options. Why don't you install Fedora 10 as a host, for example?


I use Fedora for my workstations, but wouldn't trust it as a host OS, or a server OS for that matter. Just don't feel confident in its stability at all. I prefer to use CentOS, but compile things like Apache, MySQL and PHP from source.
Quote:



Originally Posted by PCS-Chris


FYI Fedora 10 does not include host (Dom0) support.


Can you elaborate what that would mean to me? Does this mean it won't work with KVM, or Xen, or OpenVZ, or all 3?
Quote:



Originally Posted by Adam-AEC


Neither does Ubuntu 8.10 :\


Someone recommended Ubuntu 8.10 Server as it apparently had some great command line VM tools. https://help.ubuntu.com/8.04/serverg...alization.html

[Adam-AEC]

I've been looking for a distro that had a Xen 3.3 release, since I need a recent version of libvirt that has a certain library call.
Setup Ubuntu 8.10 yesterday and even tho apt has a ubuntu-xen-server meta package, it looks empty.
I haven't tried 8.04 yet (going to today) but xen-tools is installable from apt, so I imagine thats what they might be talking about. You can install xen-tools on a RHEL machine, you just need to install the Perl dependencies (and rinse/debootstrap if you are using that method)
If you don't think you'll need to vary the kernel at all, I'm sure CentOS5 will work for you. Just remember that the ramdisk that comes with it is broken for Xen, and I believe they use xvc0 for a console.
I wonder what is going to happen with Xen on Redhat, since I think they bought interests in the company that created/maintains KVM?





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