[CentOS-virt] i386 VM on x86_64 host in Xen

Tue Dec 11 18:10:01 UTC 2007
Scott Dowdle <dowdle at montanalinux.org>


----- "Karanbir Singh" <mail-lists at karan.org> wrote:
> the fact that openvz kernel does not boot my machine, takes it 
> completely out of the working category.

Not booting would be a problem. :)  The only OpenVZ kernel I've had trouble booting was one where they added Xen support (so you can use both Xen and OpenVZ on the same host).  I don't mean to associate Xen with the boot problem... the machine got stuck on USB detection and wouldn't get past that.

If you remember any of the details, it would be interesting to report the boot failure to the bug tracking system... but unless you were willing to do followup, it would just be another ticket that doesn't have the possibility of being resolved.

> Also, none of the HA tools work for me under openvz.

Here's a wiki page on using DRDB and heartbeat... although I've not done it myself.

For high availability, I just migrate my VPSes from one physical host to another periodically... and have good backups.  I know that isn't real HA but it is suitable for my needs.

I'm guessing that HA isn't a feature used by more than a single digit percentage of Xen users... but I really have no data one way or another.

Again, it's an area where if you need HA, then OpenVZ might not be for you.

> Neither is it capable of running selinux, which is another show stopped.

I'm one of those people who have yet to take the time to learn SELinux... and unfortunately, I think there are a lot of us out there.

I'm not sure if there is a technical reason why SELinux and OpenVZ are incompatible.  I've asked questions from people who should know... and the answer I get is that the main reason SELinux support is not available with OpenVZ is because of the same reason some other projects say it has to be turned off... simply because they don't want to have to deal with all of the troubleshooting involved with its use.  That's a bad excuse but it seems to be pretty common.

The vast majority of Linux distros don't support SELinux anyway... and for users of those, it isn't an issue.

>> There are uses where Xen is much better suited and OpenVZ isn't even
>> a viable option.
> Sure, thats what my point was. But my point also went on to say that 
> aprt from high density hosting, I am yet to find a role where openvz
> was a better fit. I am open to hearing about your use cases :D

Your argument is like saying everyone should drive a large SUV because it has 4-wheel drive and it holds a lot of passengers... and it has a large gas tank.  I didn't flesh that argument out very well... but my point is that not everyone wants or needs 4-wheel drive or a lot of passengers... or a large gas tank.  And OS Virtualization gets more miles per gallon. :)

I could just as easily say that a physical machine is a much better solution than Xen because you can do more with a physical machine than you can a virtual machine... but I'm guessing you see the fault with that argument.

> sure, but again, only in high desity hosting solutions. I am yet to
> see a openvz deployment outside that.

The vast majority of people I talk to on a daily basis are using OpenVZ in situations other than high density hosting solutions.   This would include myself. :)  The common misperception is that OpenVZ or OS Virtualization is only good for high density web hosting.  While that is an area where it definitely excels in, it isn't the only thing it is good for.

> Depends on the client setup, lots of people seem to rely on the amazon

I think that Amazon makes up the largest percentage of Xen deployments.  I hope they are giving back to the community.

> btw, whats wrong with virsh ? you seem to be happy using cli tools for

Nothing.  I'd like to learn more about it... especially if and when it supports OpenVZ. :)

> right, so your ideas on Xen are mostly based on the lack of awareness.
> You can quite easily control and tweak runtime resources with Xen,
> that was one of the main selling points for it in the first place.

I'll grant that.  Please point me to a web page that talks about the tweakable resource parameters of Xen.  All I am aware of are memory and number of CPUs.  Hey, I'm here to learn... that's why I signed up for this mailing list.

> Most people who do high density hosting can achieve similar results /
> density without really needing a userspace vm model. eg. I know that 
> $LargestHostingISP in .de is presently looking at howto educate the 
> users that they might actually get a better deal with almost all the 
> same resource access using shared hosting rather than VPS's running 
> UML/Virtuzzo/Xen etc. Lets see how that pans out. At the moment, the 
> idea and selling point of VPS's is that its a buzzword.

You mean service level virtual hosting (ie Apache VirtualHosting) rather than using virtualization?  That might be true... but there are drawbacks to that.  I mean, you can't give someone root access and allow them to install software, create accounts, etc.... in non-virtualized environments.  Perhaps I'm not understanding the alternative you are referring to.

I do understand that there is a buzzword aspect to "virtualization" but I'm sure I don't have to explain to you situations where it offers benefits.

Scott Dowdle
704 Church Street
Belgrade, MT 59714
(406)388-0827 [home]
(406)994-3931 [work]