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Why do people pay more for KVM or XEN?

Why do people pay more for KVM or XEN?

JunJun Member
edited August 2012 in General

I can't understand why people want KVM or XEN better than OpenVZ for Linux server. I think there aren't many people who really need KVM or XEN over OpenVZ.

The only strong point of KVM and XEN over OpenVZ I know is more isolation. But do you really need more isolation? From my personal experience, when people on same node abuses, your vps gets slower no matter if it is KVM or OpenVZ. Also, most providers load commonly used modules such as tap/tun and netfilter/iptables for OpenVZ.

AFAIK, OpenVZ has way much better performance than any other virtualization methods. As long as provider does not oversell (and that is the reason why I stick to famous providers such as buyvm or hostigation), OpenVZ seems to be the best virtualization method for common uses of server.

There was one exception in my case when I wanted to use OpenCV library and needed to load special module for better image processing. But except for those special cases, I can't get why people love KVM or XEN so much.

I believe there should be good reason that I don't know yet. Could someone tell me why?

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Comments

  • They think they're getting a premium product, and are willing to pay more for it. Which is fine, because i'm willing to charge more for it. I like money.

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  • The most common rationale I seem to read is that people believe that it's harder for providers to oversell KVM or Xen. Effectively, they're throwing money at performance. Whether or not they actually get it would be a lively discussion.

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  • JunJun Member

    @Damian said: They think they're getting a premium product, and are willing to pay more for it. Which is fine, because i'm willing to charge more for it. I like money.

    This is LowEndTalk. I hope people have good reason for what they are paying.

  • People still have that overselling argument with OpenVZ but in my eyes if managed properly it runs with less background and in turn provides a superior product -- that's just my 2 cents.

    People like shiny things, KVM/XEN seem shiner to me.

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  • Someone has told me that "Xen" sounds cooler than "OpenVZ or KVM"

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  • BigScootsBigScoots Member
    edited August 2012

    Also, fun fact, for the moment CentOS 6 dropped XEN support -- perhaps it is less shiny now?

    Also, @simplenode I believe you just made a fact.

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  • JunJun Member

    @SimpleNode said: Someone has told me that "Xen" sounds cooler than "OpenVZ or KVM"

    lol Oh please somebody give me a good reason

  • CiriumCirium Member
    edited August 2012

    @Jun OpenVZ better than Xen?

    That just ain't accurate.

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  • @Cirium said: Um. No.

    Please, continue.

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  • BSD OS and kernel/package developer? there's many reason here and out there but this both reason came in my first thought.

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  • We prefer Xen/KVM over OpenVZ because we need full control over kernel and iptables.

  • JunJun Member

    @Cirium said: @Jun AFAIK, OpenVZ has way much better performance than any other virtualization methods.

    Um. No.

    Why is that? What I know is: OpenVZ has less virtualization overhead which leads to better performance.

  • I need full iptables access

  • CoreyCorey Member
    edited August 2012

    @gbshouse @winston can't the provider enable the needed iptables modules?

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  • JunJun Member

    Some people came up with iptables... But I can't get it. I know there are some exceptional cases that special modules are needed for some special features of iptables such as mac address filtering, but for common use, most providers do load netfilters/iptables.

  • @Jun I guess it all comes down to more control of the system from more isolation from the virtualization system.

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  • JunJun Member

    @gbshouse said: not all of them

    Summer...

  • JunJun Member

    @Corey said: @Jun I guess it all comes down to more control of the system from more isolation from the virtualization system.

    Yes. I get it. But my point is - do you really need more isolation?

  • KuJoeKuJoe Member
    edited August 2012

    Somebody who thinks a container is the same as a virtual machine doesn't know the difference. ;)

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  • @Jun said: Yes. I get it. But my point is - do you really need more isolation?

    yes. especially from summer hosting who trying to do vzctl enter/exec my CTID..

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  • JackJack Member

    KVM Let's you have full control over things OVZ can't let you do.

    i.e the cloudlinux for CPanel can only be ran on XEN / KVM / Dedicated servers.

    iptables doesn't work as it should inside ovz in my experience.

  • CiriumCirium Member
    edited August 2012

    @Damian

    -Well for starters you get more access and its more isolated. -Not to mention that with openvz nothing I ever need is there. Like modules, and such. The permissions are different, so if you want module changes you have to contact your host, which in xen you dont (Example: PPP Modules), with Xen, its all just their. Which is an hour wasted out of your life trying to install stupid modules needed that Xen already has.

    -Have you tried basic things like zipping directories with multiple files inside? or moving files? Xen is ALOT faster. Even if the specs are the exact same, Xen will finish the task's alot faster.

    -OpenVZ just sucks when it comes to doing any type of gaming applications. Packet loss is higher, and as you can imagine, when playing a FPS game, you want your servers to be low packet loss, and be able to complete tasks quickly. Xen can complete these tasks in half the time it takes openvz to do them.

    Sure if your just doing webhosting, fine, openvz is perfect for you. But Xen is better in almost every way besides price.

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  • JunJun Member

    @Cirium Thanks a lot! Sounds like XEN is better options now.

  • @KuJoe said: Somebody who thinks a container is the same as a virtual machine doesn't know the difference. ;)

    Is the OpenVZ/KVM/Xen is not the same with virtual machine? Like the one we created with VMWare? Sorry to ask, because I don't know about virtualization.

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  • @BigScoots for my personal use I didn't mind OpenVZ until I've hit the wall again and again with trying to set up firewall rules, purge the cache memory, run custom kernels and so on inside an OpenVZ VM. Both Xen and KVM require more resources: Xen takes up RAM for itself to virtualize hardware and run, KVM needs better I/O performance. Xen can be a bitch to maintain since Red Hat has discontinued support for it. Xen PV offers the best resource management and a very granular control over CPU resources. OpenVZ is not real virtualization, but is more like a glorified version jails in FreeBSD. Therefore it has no overhead so there is no performance penalty for customers. Since the kernel is shared with the host OS the customer gets a bit more RAM with OpenVZ.

    So all of them have pros and cons, but all in all it comes down to this: With OpenVZ you have a slightly lower cost of hardware and software maintenance (think templates) and you can offer cheaper VPS servers.

    With Xen PV you loose some RAM to the Xen Hypervisor + some RAM to DOM 0, so for example on a 48GB server 1.5GB is gone to those two. That has to be factored into the cost of doing business. I/O Performance is great, and the virtualization overhead is minimal with Xen PV.

    KVM is what Xen HVM should have been but never was and never will be. KVM is just a kernel module, but it's so so powerful. It can do full virtualization, you can run any x86 or x86-64 inside a KVM VM, resource control is pretty good, I/O performance is horrible even with all the fancy write-back cache options for virtual machines and CPU resource control isn't granular at all, not even as much as in OpenVZ. KVM was never designed for the web hosting industry, it is an enterprise product and it was designed with over-provisioning in mind.

    If I needed virtualization on a small dedicated server 4 to 8GB RAM, I would use OpenVZ. For medium to large servers I pick KVM (I like to run FreeBSD once in a while) and for customers we use Xen PV until KVM matures some more.

    We tried to sell OpenVZ virtual servers to customers back in December when we started, and customer laughed at us. We got allot of the overselling arguments from different people, so we got rid of OpenVZ. Like any business, we are customer driven.

    One more thing: out of this trio, KVM is the easiest to oversell, not OpenVZ, so anyone complaining about OpenVZ being easy to over-provision is [insert your favorite insult here]. Here is how you can oversell KVM: - get a Xeon E3 server with 32GB RAM - get a 2TB 7200 RPM HDD - get a 64GB SSD - install CentOS 6 - set the SSD as your Swap partition - install SolusVM slave with KVM support - over-provision up to ~90+GB RAM - sit back, count your money and be prepared for an angry mob!

    KVM will use Swap when over-provisioned and treat it like real RAM.

  • Ok. We have legit reasons, I hope? OpenVZ doesn't have "internal"/"private" IPs and we need to reduce latency between our clusters as much as possible.

    OpenVZ with burst also fails with any application that uses a lot of virtual memory and memory mapped files. It just crashes. VSwap fixes it to some extent but not completely since it is still very limited.

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  • BigScootsBigScoots Member
    edited August 2012

    @vpsnodebox holy response! and my answer to it is ... yes. :)

    Customers who use a properly configured OpenVZ machine see the efficiency benefits, but it is certainly a bit finiky when starting to offer it as there are some work arounds necessary. Generally I feel its a better solution in most cases, not all. In the ones its not, that is what all you guys are for :D

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  • @Concerto49

    Any virtualization platform can have internal IP's, it's not hard to set it up.

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  • @BigScoots To be honest we will make the jump to KVM in the near future. Xen is wasteful with RAM and the official virtualization for Linux supported by both Red Hat and Ubuntu is KVM. In the upcoming version of SolusVM (in case you guys are using it) - KVM template support is added along with some improvements. The good thing is that you can easlily convert your existing OpenVZ nodes to KVM nodes without needing to reinstall everything. So KVM will be much easier to deplay in the coming month or so.

    We have to maintain our own Xen setups, test & update our kernel, etc., and so KVM would be a welcome change.

  • @PhilND said: Any virtualization platform can have internal IP's, it's not hard to set it up.

    Besides, BuyVM, which providers offer this right now? It's "possible".

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  • @vpsnodebox yeah we do use Solus and yeah we are considering a KVM switch as well, likely offer both as we have ~9 servers filled with OpenVZ at the moment, wouldn't want to turn all those folks on their heads. To much still to research, will look forward to its release before making a decision, will probably be a few months behind the release if we ever do make the switch.

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  • @BigScoots the way to do it would be to set up new servers with KVM and offer it as Premium service for those who need to run FreeBSD, Windows, etc. - so that it won't conflict with current services. You don't want to have a massive migration either on your hands :)

  • @vpsnodebox yeah Windows is really the only reason we were looking into the switch at all. We dislike Windows, but there are those few clients really hounding us to make the offering. We shall see! I swore off Windows 10 years ago :(

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  • @concerto49 said: Besides, BuyVM, which providers offer this right now? It's "possible".

    well the difference is that even if you set up internal IPs, the bandwidth transfer will still count - unlike BuyVM

  • While I love Mac OS X for desktop use, I put allot of money into this business so I will have to stick to my 48GB Windows 7 workstation for now... a Mac Pro with similar specs would be very expensive, even if I buy the RAM elsewhere.

  • jcalebjcaleb Moderator

    for me, it's just the memory accounting. and more control also.

  • @winston said: well the difference is that even if you set up internal IPs, the bandwidth transfer will still count - unlike BuyVM

    Bandwidth is just cost. I'm more concerned with latency. Database replication would fail with latency that's too high. Same with Web application clusters with sticky sessions.

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  • @concerto49 said: Besides, BuyVM, which providers offer this right now? It's "possible".

    SolusVM had this feature built in to it... but then they disabled it without telling anybody . I'm pretty sure once they add it back more people will offer it. Right now we manually assign internal IPs on request but it's not ideal since outgoing traffic still goes out the public IP without some custom iptables rules that I don't have the time or knowledge to setup.

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  • KuJoeKuJoe Member
    edited August 2012

    @ErawanArifNugroho said: Is the OpenVZ/KVM/Xen is not the same with virtual machine? Like the one we created with VMWare? Sorry to ask, because I don't know about virtualization.

    OpenVZ and vServer are containers. They use the host's kernel and aren't true virtual machines like Xen, KVM, VMWare, etc...

    A container is a "virtual server" that cannot be altered outside the limits of the host (i.e. kernel, hardware, etc...). You are very limited on what you can do to the actual resources as most of the hardware is shared with the host.

    A virtual machine can be altered just like a real server (although Xen PV is paravirtualization so it's like the middle ground for a container and virtual machine but that's another discussion). You can use different NIC and disk drivers on a virtual machine, you can run non-linux kernels on a linux host, you can assign different hardware even if the host does not have that hardware (i.e. a floppy drive). Virtual machines also have their own BIOS and allow you to utilize network booting just like a real server.

    All of that being said, I prefer OpenVZ over Xen and KVM most of the time. There are a few times when I need Xen or KVM but it's so rare that I need one these days (although I'm keeping my Hostigation and BuyVM KVMs for those rare occasions).

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  • InglarInglar Member
    edited August 2012

    @BigScoots said: People like shiny things, KVM/XEN seem shiner to me.

    Please don't be so cruel :)

    Some things just don't work properly on OpenVZ, or don't work at all.

    So there is no choice in such cases.

  • @KuJoe said: I'm pretty sure once they add it back more people will offer it.

    Well maybe we'll start using it when the time comes. Still not enough VSwap and VSwap = more cost, so KVM might still be better in our case.

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  • PhoenixVPSPhoenixVPS Member
    edited August 2012

    At least this isn't anywhere near as bad as Linux Flame Wars used to be. Linux vs. FreeBSD to this day is even worse. Virtualization Platform arguments are mild compared to that.

    @Jun The best argument that I can make for OpenVZ is that it is the ideal platform for a Low End VPS server since it won't take up any RAM for the kernel and the I/O performance is really good since it shares the same filesystem with everyone else.

  • You can't do this in OpenVZ: sync; echo 3 > /proc/sys/vm/drop_caches

    That's enough said :)

  • @Erawan : http://board.prometeus.net/viewtopic.php?f=8&t=851&sid=8c3adcbff2805f13872cc0f447a76067 First post is about virtualization types. I am also fan of OVZ when I buy, but at work use Xen, and it is not about isolation, it is simply proven mature technology that I use for years. OVZ may have more speed but Xen is not terribly slow either, especially since before I was using VMWare with it's terrible habit of writing the memory on disk... I also don't like admining OVZ, I am simply not into all those hacks to make it behave a bit like a real vm. As for KVM, well, I am not a RH fan, Xen is faster and has all I need, unlike VMWare wont become EOL or unsupported any time soon, no matter what for profit companies think. M

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  • I'm making a perhaps-fallacious logical leap here that if you can argue this hard about which is better without any clear winner, they're more or less equal except for edge cases*. People keep saying OVZ or KVM has better performance, but with no benchmarks, and nothing except "my friend said," or "this blog says," or, "I've used this one longer."


    *: e.g., Needing to run your own kernel for some reason, or iptables.

  • @Soylent said: People keep saying OVZ or KVM has better performance

    I think this one has no doubt, OVZ DOES have better performance on similar machines with similar numbers of VMs and similar load. Since it is really hard to test that in practice, there is some debate, but since KVM has WAY more overhead, then it is obvious it should perform worse. In practice, if it doesnt choke, OVZ is loaded more and more, KVM hits the wall faster. M

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  • Maounique KVM has even lower virtualization overhead than Xen PV! The real issue is its I/O performance. Since it is real visualization it tends to treat its partition on the LVM as a real hard drive, so it will read and write only in-between the start and end sectors. KVM by itself is just a puny little Linux Kernel module.

  • jcalebjcaleb Moderator

    i think the factor to choose which is on what you will use your vm for.

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