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Performance Evaluation of Xen Vs. OpenVZ
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."
[Xen]... "trades off performance for much better isolation and security."
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.
Kernel VM is based off QEMU -- but doesn't Xen have a similar hypervised Linux kernel. (I personally thought that may be why KVM was created -- to be a better Xen.) As I'll eventually upgrade to a Linux distro with KVM, I wonder if there are similarities in them -- or preferably if KVM could be fully tested and compared with these results.
" hypervisor-level virtualization technology that allows multiple operating systems to be run with and without para-virtualization "
I don't know about you but it still makes my eyes hurt!
09 F9 11 02 9D 74 E3 5B - D8 41 56 C5 63 56 88 C0 45 5F E1 04 22 CA 29 C4 93 3F 95 05 2B 79 2A B2
Zen's performance issues were fixed by Avon, under Orac's guidance.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Hypervisor — the software that makes the virtualization happen... sometimes means virtualization that runs on bare-metal, rather than under a host OS.
Paravirtualization — 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."
From reading the article on hypervisor it still seems ambiguous. It implies that a hypervisor is not exactly a VM but the actual detailed description makes it out to be a VM. Others seem to imply it means the VM is running as an OS basically.
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.
As somebody that actually has experience setting up and running virtualized systems (I work for a web hosting company) let me add my two cents here.
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.
Does it run multiple instances of Linux?
Nothing like a virtualization comparison that ignores the 800 guerilla that is VMWare. How do the learning curves, performance and security of these products compare with VMWare? Why should someone who is satisfied with VMWare consider other alternatives?
the clock on the wall says 4 til 7
Here are a few talking points based on my experiences with both Xen and VMWare (ESX Server & Workstation).
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 $30,000. Assume an additional 40-80 hours of learning to get up to speed with Xen vs VMware.
The comments above cover the open source / free version of Xen. I have no experience with the commercial Xen offerings.
Personally i'm Xen biased due to cost.
Linux has a lot of great VM options. VMware is a great free (cost) option, and KVM has become a great option very quickly. OpenVZ and VServer are interesting light weight OS "jail" virtualizations. They each have pros and cons, depending on your requirements and apps being used.
I'm setting up my "next generation" home linux server, and looking into the virtualization options for that. Probably a bigger factor than performance is the setup and manageability. I have found Xen to be pretty primitive compared to VMWare.. setup is a pain, documentation is spotty, and support is minimal. The one advantage of Xen is that you can (and often must) do everything with it from the command-line. The GUI tools are weak at best.
I am now leaning towards using VMWare server. But, I still need to do some testing with KVM.. articles I have read about it sound very impressive. KVM paravirtualization performance is supposed to be excellent. But, I don't know about management.
Go the FreeBSD way!
Lousy virtualization, Happy users: FreeBSD's jail(2) facility
Source: UKUUG
Tags: ukuug, presentation, freebsd, jails, poul-henning kamp
Slides (2.7 Mb)
Lousy virtualization, Happy users: FreeBSD's jail(2) facility by Poul-Henning Kamp (phk@FreeBSD.org)
bash$
It's not always about performance; Xen gets each their separate kernel. This means that special adjustments can be made for a virtual machine. Also, with Xen you could easily experiment with an upgraded kernel for the virtual machines, without rebooting the main (host) machine. Finally, I for myself like the fact that you have your 'own' kernel. It feels much more like a real machine. Especially with a bootloader like pygrub, which is employed in RedHat AS and CentOS, the kernel inside the virtual machine can even be upgraded by yum running inside the VM.
Note that I'm not a Xen apologist, I'm not denying a performance hit here.
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OpenVZ is somewhat like FreeBSD Jails. It provides some separation which makes it easier to manage multiple complex servers. For example, it makes sense to run a web server and mail server in two separate virtual machines, since it keeps the configuration independent.
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.
Excuse me, but please get off my Pennisetum Clandestinum, eh!
We're using HyperVM from LxLabs http://www.lxlabs.com/ and it manages both OpenVZ and XEN. You can easily watch the performance penalties of both virtual machines from the same panel and migrate in between. So whenever someone abuses OpenVZ you can migrate it to XEN.
qemu runs Win2k. My AMDX2 3800 runs it using kqemu. I happily use it for testing things in I.E. It seems about as fast as my PIII 1Ghz laptop, though I've never actually measured it.
There are places where the networks are not touching,and there are places where they are-Boeing's Lori Gunter
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 for some more details.
-- Kir Kolyshkin, OpenVZ project leader.
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 migration feature, although I haven't tried it.
-- Kir Kolyshkin, OpenVZ project leader.