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Performance Evaluation of Xen Vs. OpenVZ
Posted by
kdawson
on Mon May 14, 2007 08:28 PM
from the price-to-pay dept.
from the price-to-pay dept.
An anonymous reader writes "Compared to an operating-system-level virtualization technology like OpenVZ, Xen — a hypervisor-level virtualization technology that allows multiple operating systems to be run with and without para-virtualization — trades off performance for much better isolation and security. OpenVZ's performance advantage due to running virtual containers in a single operating system kernel can be significant. A performance evaluation study (PDF) done by researchers at the University of Michigan and HP labs provides insight into how big a performance penalty Zen pays and what causes the overheads (primarily L2 cache misses)." From the report: "We compare both technologies with a base system in terms of application performance, resource consumption, scalability, low-level system metrics like cache misses and virtualization-specific metrics like Domain-0 consumption in Xen. Our experiments indicate that the average response time can increase by over 400% in Xen and only a modest 100% in OpenVZ as the number of application instances grows from one to four... A similar trend is observed in CPU consumptions of virtual containers."
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Stop the press (Score:3, Insightful)
No kidding, that's why I use it! Xen's performance ain't so bad. Show me a better performing virtualization solution that matches or bests Xen's isolation security - then we'll talk.
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Re:Stop the press (Score:5, Insightful)
So to sum, we've got OpenVZ, Virtualbox, KVM/Qemu, Xen, VMWare, Virtual Iron, and Virtuozzo. With so much virtualization software, I personally think performance takes a back seat to functionality (sure OpenVZ is fast, cool, what will it do for me that VMWare or Xen won't?). Is there really that much space in the virtualization landscape?
Parent
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Re:Stop the press (Score:5, Interesting)
Yeah but Xen is still a royal PITA to get running. KVM wasn't bad, and VMWare was pretty easy. I haven't even seen OpenVZ.
Yes, Xen is harder to install. But to compare it with KVM ... did you try to use them? KVM (at least, last time I tried -- which was only a couple weeks ago) is still in development, and the performance is so low compared to Xen that it's not even funny.
On the other hand, VMware is very nice, specially the free Server edition, and it's really easy to use. But even so, performance is better in Xen. Check this [xensource.com]. Paravirtualization needs modified guests, but the outcome is so good that VMware is trying paravirtualization too [vmware.com].
VMWare is so far ahead it will take some time for Xen to be considered out of the hobbyist market and in the commercial one
What do you think is needed for Xen to be considered apt for commercial use? Remember that Xen can use unmodified guests if the hardware supports VTX/SVM instructions, which means that it can run Windows. Pretty front-ends? Xensource (which is slashdotted now, I guess, because it times out from here) offers one, and you also have Enomalism [enomalism.com].
Besides, by what Wikipedia says about OpenVZ [wikipedia.org], it seems to be more a solution like jails [wikipedia.org], because it uses the same kernel for both the host and the guest systems. The phrase "glorified chroot" comes to mind, though I'm aware that it's more than that (just adding it for the sake of trolling, I guess :-)). Xen, VMware and QEMU/KVM are, on the other hand, real virtualization solutions, where all the virtual system runs completely isolated.
I wouldn't recommend Xen for home use (VMware Server is a better and easier option, IMHO), but saying that it's not ready and comparing it to QEMU/KVM is almost a joke.Parent
Re:Stop the press (Score:4, Informative)
VMWARE is an excellent DR/BC solution due to complete virtual machine portability. However consolidation ratios (8:1 maybe) and performance are not that great, for consolidation you've probably only saved a few Us, but you have not really helped reduce the support burden, you'll still need lots of middleware / server management software to manage your estate. To actually get the most out of the DR/BC solution you also need an FC SAN and the complete Virtual Centre suite. If you've that kind of money to throw around then clearly you are in it for BC/DR purposes and VMWare is the right option. At this level you don't care if your consolidation ratios are 1:0.9 or worse.
Virtuozzo/VZ on the other hand wins hands down for consolidation and management; you can easily fit 20-30 or more VPSes on a single server; and whatever the consolidation ratio the responsiveness will always be better than the same server under VMWare. However there are some drawbacks, Virtuozzo doesn't give you complete portability; you can only host Windows 2003 guest servers on a Windows 2003 hardware node for instance and you are unable to install device drivers. Adding a new VPS takes about as long and uses about as much resource as creating a new user on a system.
I use both solutions; each definitely have their own place and couldn't be more different in their relative strengths.
Jason
Parent
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Jason.
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OpenVZ is easy to setup (once you get the kernel and packages setup, which is a breeze in Debian 3.1 and 4.0). It runs ridiculously fast, it consumes little memory, and takes little disk space (which can be furthe
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Yeah but Xen is still a royal PITA to get running.
If you think that Xen is a "royal PITA" to get running, then how do you manage to work with a server? There is a slight learning curve, but after that it's extremely easy to deal with. Much like most Unix things. The massive performance benefit that Xen gives over VMWare Server (the only one I use) is well worth the hour it takes to learn the basics.
Now, if you're virtualizing a desktop system, VMWare rocks. I use it daily for this. But after using both in production, Xen clearly has a significant perf
KVM (Score:2, Insightful)
Looks like analyst talk (Score:3, Funny)
I don't know about you but it still makes my eyes hurt!
Re:Looks like analyst talk (Score:4, Informative)
Hypervisor [wikipedia.org] — the software that makes the virtualization happen... sometimes means virtualization that runs on bare-metal, rather than under a host OS.
Paravirtualization [wikipedia.org] — I think this just refers to the cases where the guest OS is modified/recompiled to run work without needing to run in Ring 0, and instead changes those to be explicit calls to the virtualization software.
So translated, I think that means "virtualization software that runs on bare-metal, both using unmodified guest OS's, and modified guest OS's."
Parent
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From everything I can see though the word is useless and it amounts to the equivalent of computer scientists being fussy. VM or VM OS are better choices.
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> I don't know about you but it still makes my eyes hurt!
Really, it's not that complex. The technology monitors all system calls, and makes a judgement call - if it's safe to let it through, it routes it through the EPS conduits. If it's not, it routes it through the GNDN tubes. As long as you don't overload the EPS taps, it's all good.
Oblig. Nonsensical reference (Score:5, Funny)
Zen's performance issues were fixed by Avon, under Orac's guidance.
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Both are good. (Score:5, Informative)
OpenVZ is ok if all of your child environments run the same OS and you don't care about them stealing each other's resources. We constantly have problems with customers overloading their VPS and causing problems with the other environments, this doesn't happen with Xen. I've fork bombed child environments and caused the load to spike to over 700 until it crashed, dom0 and the rest of my domUs just kept running like nothing was even happening.
OpenVZ also wins if you want to oversell hardware, Xen doesn't have "burstable" memory like OpenVZ does. Personally I prefer Xen for the jailing that it does and you can also run multiple OSes at the same time. I have a server at work that's running CentOS, Windows 2003, Windows Longhorn, and Gentoo all at the same time, OpenVZ only lets you run Linux on Linux.
Re:Both are good. (Score:5, Informative)
The big difference between Xen and OpenVZ comes down to what openvz calls "privvmpages" - memory that is claimed by running processes but not actually used.
The example here is this: two OpenVZ virtual environments (VE) can be set up on a server with, say, 1 gig of ram, with a gig of swap underneath it (So, RAM+Swap equals 2 gigs).
Those two virtual environments can be "oversold" in the amount of privvmpages they're allowed to use, because processes ask for more memory than they _actually use_ all the time. So let's say we give those two VEs 1.5 gigs of privvmpages (total of 3 gigs - more than RAM+Swap), but we only give them each 500 megs of oomguarpages. (less than RAM+Swap).
The thing that _should never_ go over RAM+Swap is oomguarpages (out of memory guaranteed pages) - pages of memory that are guaranteed (OpenVZ measures some of its resources in pages and some in megs).
With Xen, on that server I just described you're locked in - there's no bursting, and there's no dynamic allocation going on. You give one domU 750 megs of ram and you give the other domU 750. That's it.
Parent
Re: (Score:3, Insightful)
Remind me to never EVER hire you to do any work for me. Ever heard of "the right tool for the job"? I am a huge fan of virtualisation, and have been using it for years, VMWare mostly, but lately more and more with Xen. Given that Xen simply does not yet play nice with most of the lower cost hardware, and has several significant shortcomings in real-life enterprise production environments (running
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OpenVZ also has a very distinct advantage - all processes in guest VEs are visible to the tools on the main host.
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Logged in one day and nothing worked. The host had changed to Virtuozzo. They tried to sell us on the advantages 'look it has a cool web based frontend' they said. It sucked. It had lower bandwidth, lower memory available and was as slow as molasses (like the load average never went below 4 on an idle system running nothing else).
We coped with that for abou
Yes, but ... (Score:4, Funny)
Re:Yes, but ... (Score:4, Funny)
Parent
And... (Score:5, Insightful)
Re: (Score:3, Interesting)
How should someone who is satisfied witn VMWare decide whether an alternative would be an improvement? When the license terms for VMWare prohibit any benchmarking its kind of hard to make a decision.
Re:And... (Score:4, Insightful)
Do I get a Karma bonus for conceding someone's point?
Parent
Re: (Score:2)
Meaning that, any methodology which favours anything other than vmware will not be approved. In this case, i think the lack of available benchmarks says more.
Xen vs VMware - personal experience (Score:5, Informative)
1. Cost - no contest, xen wins hands down $0 vs $5000/cpu.
2. Performance - xen wins noticably, i can get away with running 8 virtual machines with 1/4 the hardware that VMWare required for 6.
3. Capabilities - VMware versions ESX GSX and up beat Xen in ease of use and flexibility, anything less and Xen wins. Xen does have a quicker live migration capability, but falls short on conencting external hardware to the virtual machine (something that is trivial in VMware).
4. Stability - about even, maybe Xen. I've seen ESX crash once, and have never seen Xen crash.
5. Ease of use - VMWare no question. Theres a learning curve to Xen and setting up new VM images is a pain. (which is disappearing) There are fantastic tools for VMware that will let you manage virtual machine creation and even migration from a physical box. (some of which can be used to feed xen too =))
The bottom line. A Xen setup (using open source version) that can easily run 12 VMs costs about $2,000 on DIY hardware. A VMWare server/software combo to do the same? about $30,000. Assume an additional 40-80 hours of learning to get up to speed with Xen vs VMware.
The comments above cover the open source / free version of Xen. I have no experience with the commercial Xen offerings.
Personally i'm Xen biased due to cost.
Parent
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Personally i'm Xen biased due to cost.
I agree. Just a little addition: besides, VMware licenses are even more important when you want to scale. Say you want to use two quad boxes for load balancing, running VMware in each: that's about 8 x 5000 = $40000 in licenses (or $35000 if the first CPU is for free; I'm using your prices, but I knew about a similar project where VMware was decided against due to licensing costs too). You can buy more hardware with that money and train all your staff to understand
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Tell me more, please. Looking at the Xen performance paper, it looks like Xen & VMWare are pretty close, performance-wise. The most they ever show is a 23% boost on a couple tests - nowhere near the "1/4 the hardware". Not trying to bait, but honestly curious.
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There's one item you didnt list, though it might be folded under capabilities or ease of use...
Manageability is a key item for these types of setups. As people being to depend more and more on virtualization technologies (whatever those might be) and roll out virtualized production environments, you have to figure out how to monitor and manage them. This is one area where VMWare currently has the upper hand, as Xen's management API has not yet been stabilized.
The reason this is important is because with all
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Quite simply, a corporation is going to buy VMWare Virtual Infrastructure. So the performance isn't as good? So what? Throw hardware at it. It works.
We have a significant investment in VMWare VI3 where I work, and it's great. We run it on high-
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Going off on a slight tangent, VMware Workstation (non-free, $$) is the only one that has a glimmer of (imperfect) DirectX support, although there are rumors about similar support in the forthcoming OS X version. This is important for home users (not enterprise or business users) that run windows to play real-time 3D games. ;-)
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Why would vmware compare xen to an old version of vmware? That seems rather fishy... You'd think they would want to compare xen to their latest and greatest
Re:And... (Score:4, Informative)
This is a bit out of date, but here is some comparison between Xen, User Mode Linux, and Vmware 3.2 (which is the most recent version that allows publication of benchmarks).
http://www.cl.cam.ac.uk/research/srg/netos/xen/pe
Xen is always faster than Vmware, with the exact amount varying depending on the specific load. They've all improved since then, of course.
Parent
Other VM options.. (Score:3, Informative)
I'm setting up my "next generation" home linux server, and looking into the virtualization options for that. Probably a bigger factor than performance is the setup and manageability. I have found Xen to be pretty primitive compared to VMWare.. setup is a pain, documentation is spotty, and support is minimal. The one advantage of Xen is that you can (and often must) do everything with it from the command-line. The GUI tools are weak at best.
I am now leaning towards using VMWare server. But, I still need to do some testing with KVM.. articles I have read about it sound very impressive. KVM paravirtualization performance is supposed to be excellent. But, I don't know about management.
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That's what I thought, too. Until I installed CentOS [centos.org] (*the* RedHat Advanced Server clone). Start virt-manager, click Create, click next-next-finish and voila, you have a window showing an installation.
Lousy virtualization, Happy users... (Score:3, Informative)
Lousy virtualization, Happy users: FreeBSD's jail(2) facility [ukuug.org]
Source: UKUUG [ukuug.org]
Tags: ukuug, presentation, freebsd, jails, poul-henning kamp
Slides (2.7 Mb) [ukuug.org]
Lousy virtualization, Happy users: FreeBSD's jail(2) facility by Poul-Henning Kamp (phk@FreeBSD.org)
It's not always about performance (Score:5, Informative)
Note that I'm not a Xen apologist, I'm not denying a performance hit here.
Appples and oranges... (Score:4, Interesting)
Xen, is like VmWare or Qemu and provides an independent virtual machine for each system. These systems can be anything at all: Windows, Linux, BSD, whatever.
Performance wise, OpenVZ is bound to win, because it is a different solution to a different problem.
Hypervisor for both (Score:2, Interesting)
Much better isolation and security? Hmm... (Score:3, Interesting)
I guess I have to correct you here. Xen trades off performance for an ability to run different kernels, and this has nothing to do with either isolation or security. So, Xen is good when you want to run different kernels (different OSs).
OpenVZ, on the other hand, employs a single kernel model, which makes it suitable for you if you only want to run Linux (different distros are possible, different kernels are not). But in this very field OpenVZ is way better than Xen -- not only in terms of performance, but also scalability, manageability, density, and usability.
Speaking of isolation and security, OpenVZ runs on thousands of ISP/HSP servers, and everyone can buy a VE (Virtual Environment) for about 10-15 bucks a month. There one have a root account and can try to exploit the system in all the possible ways. So far those HSPs are not out of business yet, that practically proves the system is secure and properly isolated. More to say, security comes from the constant care, and we (OpenVZ team) do care for security a lot, see this blog entry [openvz.org] for some more details.
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OpenVZ and Virtuozzo rely upon Linux kernel modifications; in other words, no FreeBSD, no Windows.
VMWare is who they are going after (Score:2)
I am a big fan of Virtuozzo and OpenVZ. I just wish vzstat would be included with the free stuff.
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In fact, free OpenVZ has most of what you tell about VMware. Live migration is here, and it does not require to have a SAN or a dedicated NIC, or pay for vmotion. High availability with clustering can be set up (see here). And finally, you don't have to pay a performance penalty if you want virtualization.
The commercial product based on OpenVZ (i.e. Virtuozzo) has all that plus web-based and gui management tools, P2V migration tools etc. etc.
It also makes sense to point out that Xen also has a live migr