Command Center

We vote for Xen we are running small VPS hosting company and I can say xen is the best virtuazliation ever we added http://hostbillapp.com to vps provisioning and we are reall happy for that.

This whole thing is rubbish - show benchmarks on the same hardware with the same loads.

So far the only empirical evidence presented is the HP study which says OpenVZ is faster.

I am not pro MS nor pro VZ, but in this case you have not presented anything other than circumstantial claims that Xen is better. Justify it.

I've enjoyed reading other parts of this sites, but this particular article is utterly pointless because you gave zero indication what kind of hardware these servers were on.
If you compare an OpenVZ machine that shares a slow single core CPU between 10 VMs to a dedicated server with two quad cores of course the VZ is gonna loose.
Since you didn't give ANY information about hardware we have to assume that the differences you noted are entirely down to having stronger hardware in the Xen and the dedicated servers :(

Xen just can not be faster than OpenVZ/Virtuozzo, that's nonsense.

Apparently in those cases you haven't configured OpenVZ/Virtuozzo resource management properly, thus applications experienced resource shortages which is the reason of the slowdown.

Let me give you a clear example: it's like driving a sport car with manual gearbox, using only the low gear. The problem of slow car is you have to upper the gear while you increase the speed. Instead, you use a truck, and now claim that the truck is faster.

This article should help: wiki.openvz.org/Resource shortage

Well, at the risk of flogging a dead horse, I think any discussion about virutalization comparisons should reference:

http://wiki.openvz.org/Introduction_to_virtualization

My understanding is that OpenVZ/Virtuozzo is fundamentally different from Xen in how it does 'virtualization', so really, the issue is whether either technology is somehow more appropriate to Drupal. Obviously, generic comparisons can be made in favour of either, depending on your setup.

I think it would be fair to say that most of the time, there's no significant difference. I would guess that if the server's not overloaded, chances are VZ would have a slight edge. I think the key question your tests raise is: does Xen handle overload better? I'd bet your examples don't demonstrate this at all, but it's still a fair question.

From looking at your various examples, I'm going to wager that Xen degrades better because it can guarantee resources - i.e., the server can't get clobbered as easily by another virtual server on the same physical machine.

The flip side of this is that if you're lucky enough to have a VZ server on a mostly empty machine, then you can take better advantage of it.

So, if you've got issues running Drupal on a server and it's a VZ virtualization, moving it to Xen will probably work, but only because you're changing hosts!

You can not compare XEN with OpenVZ without detailed comparison of resources allocated to the virtual host. OpenVZ vm's by default are installed with very little resources and sometimes it is even impossible to install larger software - like java into those.

Therefore you need to examine /proc/user_beancounters and make sure that there are not any bottlenecks for your application.

Look in OpenVZ wiki for more information:
http://wiki.openvz.org/Resource_shortage

Out of interest - I noticed that you said that in the second case, you installed the problem site on a Xen VPS. However it was not clear that the Xen and OpenVZ site instances were hosted and benchmarked on the same machine. If not, then I don't think you can really compare the results, since even the best resource scheduling can't make Xen on a dedicated unloaded server compete with OpenVZ on an underspecified shared server that happens to host a porn network ;)

We run some OpenVZ VPSs and find them very fast (well, pretty much as fast as the raw hardware...if you get better than that something is wrong!). Most things I read seem to indicate that OpenVZ has a much lower overhead, and most better resource management when under pressure (especially because of the two-level scheduler). While your results are interesting, they do seem a bit anecdotal to me :)

For example, here is part of the conclusion from the HP Xen vs. OpenVZ study.

For all the configurations and workloads we have tested, Xen incurs higher virtualization overhead than OpenVZ does, resulting in larger difference in application performance when compared to the base Linux case.

Performance degradation in Xen increases as application workloads increase. The average response time can go up by over 600% in the single-node case, and between 115% and 600% in the two-node case depending on the number of applications.

For all the cases tested, the virtualization overhead observed in OpenVZ is limited, and can be neglected in many scenarios.

For all configurations, the Web tier CPU consumptionfor Xen is roughly twice that of the base system or OpenVZ. CPU consumption of all systems and all containers goes up linearly as the workload increases. The slope of increase in the case of Xen is higher than in OpenVZ and the base cases.

Workhabit mention the same observation on Xen vs. Virtuozzo, in this article.

And here are some benchmarks of Xen vs OpenVZ.
--
2bits -- Drupal consulting

I moved to linux-vserver. These servers are for one organization on dedicated servers. Not vps for rent to others. So not really like the situation in your post.

It is a chroot environment more like bsd jails. For my usage having the same kernel is not an issue. There is good support in Ubuntu and debian too.

http://en.wikipedia.org/wiki/Linux-VServer

Joe

agree with you. I use vservers on my productive servers for some months, they now eat less system resouce compared to xen. Additionally...
1, as for my exp.,vserver is much easier to manage.
2, openvz is nearly the same as vserver, there's no absolute difference.

They all work from a functionality point of view, whether it is OpenVZ/Virtuozzo, Xen, UML, or Linux Vserver.

My point was performance. Xen is far superior over OpenVZ. How does Linux Vserver fare in this regard in your case?
--
2bits -- Drupal consulting

I was moving from self-hosted user-mode-linux and a couple of rented vps accounts on uml too. There was a little performance lag on them but mostly a stability problem on the ones I hosted on our dedicated servers. UML development had slowed and seemed to have been leapfrogged by these others.

I did not benchmark agains Xen but part of the decision making process was because the Linux-Vserver architecture could have performance advantages. It runs only one kernel for all virtual servers. The files in each virtual server are not in some COW like image so there isn't a slowdown there either.

I'm going to try Virtualbox on my development desktop to see how it works.

good subject again Khalid, thanks.

Joe

I have to back up Khalid here. We are former SW-Soft Gold partners, and were involved with OpenVZ from as far back as having made the suggestion to them to not call it OpenVirtuozzo due to brand confusion. ;-)

We have a massive cluster (several racks full) of XEN now running Drupal-based applications, and have found that in benchmarks, XEN and even VMWare bench far more reliably than OpenVZ and Virtuozzo.

The performance question is secondary to the fact that we can get consistent results using VMWare and XEN (we use XEN now almost exclusively, VMWare only for very large clients or those with a specific requirement).

It's the consistency that matters, because what you want to avoid is a couple of higher performance sites on a box crushing your performance when they get busy - that's something you don't get with "soft virtualization" systems like Virtuozzo, OpenVZ, or, sadly, even LVS (though proper architecture more than makes up for this with LVS). The only real sore point with Xen is the same point with any virtualization system - i/o constraint.

This isn't really a problem until you start running intensive database-driven applications, which includes Drupal. Then you start getting into the joy of "which system-tuned variable gets crushed first" with soft virtualization systems.

This isn't to say it can't be done, but default settings won't do it, and it's a LOT harder than just grabbing yourself a sliced up "hard virtualization" style box (XEN, VMWare, etc).

As usual Khalid, nice comments.

My 2c.

Jonathan Lambert
Principal & CEO

WorkHabit, Inc.
http://www.WorkHabit.com/
http://www.WorkHabit.org/