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Thread: Xen vs OpenVZ

  1. #1
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    Xen vs OpenVZ

    Hi,

    I'm interested in hearing thoughts on OpenVZ vs Xen for web hosting - from the point of view of both a host and a user?

    Which is better / faster / more reliable / easier to maintain?

    Thanks,

    Ian

  2. #2
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    They both have their pros and cons. It really depends on what you want to do and how you want to do it as to which one will work for you.

    I can equate your question to asking "Which web hosting provider is the best?" ... there is no "best" but only the one that is best for you and your particular needs.

    If you can tell us what you want/plan to do we can likely give you better advice.
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  3. #3
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    I prefer OpenVZ, custom OpenVZ control panels have the ability to do so much more in my opinion.

    Also OpenVZ is more "native" speeds, then Xen.

    Also, if you have a VPS, do you "Really" need to have a custom kernel?
    Steven Crothers
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  4. #4
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    Quote Originally Posted by Crothers View Post
    I prefer OpenVZ, custom OpenVZ control panels have the ability to do so much more in my opinion.

    Also OpenVZ is more "native" speeds, then Xen.

    Also, if you have a VPS, do you "Really" need to have a custom kernel?
    Xen provides better isolation and dedicated memory, OpenVZ uses a shared kernel approach so resources are more shared.

    This provides benefits for both, users are "less" likely to affect others in Xen due to not being able to oversell and more isolation however it can still happen especially with disk i/o.

    OpenVZ is faster as stated because it requires less overhead with the shared kernel approach but overselling can give its advantages and disadvantages. The obvious, overselling can cause poor speeds which is why OpenVZ has a bad rep around here because too many hosts oversell.

    I'd say OpenVZ also has much better documentation and ease of use.

  5. #5
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    You may also have a look about this recent thread about the topic here: http://www.webhostingtalk.com/showthread.php?t=912557

    heaps good insights from experienced Linux Admins.
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  6. #6
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    OpenVZ you can oversell, Xen you can't
    Xen has a lot more operating system options (With HVM-ISO), where OpenVZ is just things running the same linux kernel
    Both have fantastic control panels (personally i prefer SolusVM which supports both OpenVZ and Xen)
    I find the CLI tools with OpenVZ a lot easier to use then Xen, but i'm just learning the Xen ones currently

  7. #7
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    You can search these forums and see this topic discussed numerous times. I like Xen myself but I have never had any issues with OpenVZ host that was related to the technology. Quality hosts manage their servers properly so I never had a problem.

  8. #8
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    I'd choose OpenVZ It is much more easy for customizing & operating

  9. #9
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    Quick Summary.

    Xen = paravirtualization (virtualizes the kernel) vs OpenVZ = OS-level virtualization
    As a result, Xen is more flexible but OpenVZ has lesser overhead.

    Xen = true memory accounting with swap vs OpenVZ = accounting memory allocated
    As a result, OpenVZ often over accounts for RAM that is allocated and not used.
    For example, a java application will likely fail in a 512MB OpenVZ container but succeed in a 128MB Xen container as java loves to allocate alot of memory.
    Furthermore, OpenVZ permits (and makes it easy to) overselling, Xen does not.

  10. #10
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    Quote Originally Posted by tsj5j View Post
    Quick Summary.

    Xen = paravirtualization (virtualizes the kernel) vs OpenVZ = OS-level virtualization
    As a result, Xen is more flexible but OpenVZ has lesser overhead.

    Xen = true memory accounting with swap vs OpenVZ = accounting memory allocated
    As a result, OpenVZ often over accounts for RAM that is allocated and not used.
    For example, a java application will likely fail in a 512MB OpenVZ container but succeed in a 128MB Xen container as java loves to allocate alot of memory.
    Furthermore, OpenVZ permits (and makes it easy to) overselling, Xen does not.
    What happens when a given OpenVZ host doesn't oversell and doesn't offer burst RAM over OpenVZ ? I use one host here with nice CPU-intensive application that loves to eat all the ram (like java), and still no memory conflicts and corruption (app. uptime = 25 days now). Other OpenVZ's offen cause my app to get corupted and fail over time. Over Xen this specific application causes almost any host to kick me out (i didn't seen a host that will tolerate 25% load of a HT CPU core for constant period).

  11. #11
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    Hi,

    Thanks for the replies.

    What i'm wanting to do is Apache, MySQL and PHP web hosting - separate sites out across multiple VM's rather than virtual host them on the same server.

    Which is most suited to that?

    Which is going to give the best performance?

    What's going to happen if a site comes under high traffic under both of them?

    Does not having swap not cause a problem for OpenVZ? - doesn't it start running out of memory and fall over?

    Thanks,

    Ian

  12. #12
    OpenVZ is generally the most cost effective solution for virtualization.

    Your hosting needs are pretty standard, you dont need custom kernel hence my advice is you should go for OpenVZ.

    OpenVZ is basically faster than Xen when not oversold and when high memory swap is not required.
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  13. #13
    I'd also say a big consideration is that if you're managing VMs yourself use OpenVZ.

    For unmanaged VMs, Xen offers true isolated virtual partitions, so even if someone tries to wreck it, it doesn't affect everyone else on the same server.
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  14. #14
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    you might want to look at this thread also, this is a real live case of someone who got his VPS down due to another "bad user" on the same hardware node.

    http://www.webhostingtalk.com/showthread.php?t=928090

    the true answer is - whatever is easy for you to manage would be the best choice all do the same basic job :-)

  15. #15
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    Quote Originally Posted by danceboysf View Post
    What happens when a given OpenVZ host doesn't oversell and doesn't offer burst RAM over OpenVZ ? I use one host here with nice CPU-intensive application that loves to eat all the ram (like java), and still no memory conflicts and corruption (app. uptime = 25 days now). Other OpenVZ's offen cause my app to get corupted and fail over time. Over Xen this specific application causes almost any host to kick me out (i didn't seen a host that will tolerate 25% load of a HT CPU core for constant period).
    I think you completely misunderstood the differences when I stated.

    I said that the same application with high allocative tendencies (eg. java) will reflect a much higher memory usage in OpenVZ compared to Xen, meaning you need to upgrade to a higher plan = more money lost.
    This does not mean that OpenVZ is less reliable.

    And, whilst Xen doesn't allow overselling, it does allow you to put 16GB RAM on say, a Pentium III processor. So naturally it isn't overselling but your performance is still crap.

    Hence, if the same host offers Xen and OpenVZ at the same time, I'd go for Xen without a second thought.
    But if a crap host offers Xen and a reputable host offers OpenVZ, I'd still go for OpenVZ.

  16. #16
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    Hi,

    Thanks for the comments!

    It seems to me that if you are renting a VPS from a provider then it's a better/safer bet to get Xen (but more cost effective for the provider to run Xen).

    If you are running your own VM's then OpenVZ seems a better choice (as long as the application doesn't require a specific Xen feature like a custom kernel).

    Is that a fair assessment?

    Thanks,

    Ian

  17. #17
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    Thanks all for your replies in this post, it helped me to understand more about the differences in these vps solutions.
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  18. #18
    Quote Originally Posted by tsj5j View Post
    I think you completely misunderstood the differences when I stated.

    I said that the same application with high allocative tendencies (eg. java) will reflect a much higher memory usage in OpenVZ compared to Xen, meaning you need to upgrade to a higher plan = more money lost.
    This does not mean that OpenVZ is less reliable.

    And, whilst Xen doesn't allow overselling, it does allow you to put 16GB RAM on say, a Pentium III processor. So naturally it isn't overselling but your performance is still crap.

    Hence, if the same host offers Xen and OpenVZ at the same time, I'd go for Xen without a second thought.
    But if a crap host offers Xen and a reputable host offers OpenVZ, I'd still go for OpenVZ.
    Great post. 100% agree with you.
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  19. #19
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    Quote Originally Posted by ichilton View Post
    Hi,

    Thanks for the comments!

    It seems to me that if you are renting a VPS from a provider then it's a better/safer bet to get Xen (but more cost effective for the provider to run Xen).

    If you are running your own VM's then OpenVZ seems a better choice (as long as the application doesn't require a specific Xen feature like a custom kernel).

    Is that a fair assessment?

    Thanks,

    Ian
    Yes. Xen is basically better but requires a provider that is knowledgeable enough not to screw it up.

    Xen installations are slightly more complex than OpenVZ, which is partially why Xen is significantly rarer.

  20. #20
    There much more Linux templates for OpenVZ than for XEN as I see it.
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  21. #21
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    Quote Originally Posted by cloudvps View Post
    There much more Linux templates for OpenVZ than for XEN as I see it.
    Thanks for proving my point, this is precisely what I mean.

    Some OpenVZ providers (not all, I'm just saying SOME) have little, if any knowledge of what's going on behind the scenes. OpenVZ simplifies the process alot, whereas Xen does not.
    In the above mentioned example, just because there are more OpenVZ linux templates does not make it more flexible.

    If there is a need for it, it is not hard to make custom Xen templates at all.
    Furthermore, Xen permits for Windows and other OSes due to its level of virtualization, whereas OpenVZ is restricted to Linuxes.

  22. #22
    Windows is the known limitation of OpenVZ, of course, if you plan to deploy Windows images OVZ is not for you.
    I would use WindowsOS host with Virtuozzo for that purpose.
    Also, from what I know, KVM has pretty good performance with Windows guests.
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  23. #23
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    Quote Originally Posted by tsj5j View Post
    Thanks for proving my point, this is precisely what I mean.
    Classic - you couldn't have even planned that better

    Ian

  24. #24
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    Quote Originally Posted by tsj5j View Post
    Thanks for proving my point, this is precisely what I mean.

    Some OpenVZ providers (not all, I'm just saying SOME) have little, if any knowledge of what's going on behind the scenes. OpenVZ simplifies the process alot, whereas Xen does not.
    In the above mentioned example, just because there are more OpenVZ linux templates does not make it more flexible.

    If there is a need for it, it is not hard to make custom Xen templates at all.
    Furthermore, Xen permits for Windows and other OSes due to its level of virtualization, whereas OpenVZ is restricted to Linuxes.
    My opinion is not professional, it's based on my personal experience. I've deployed a project soon on a OpenVZ based host.
    And guess what - the result is a lot better from what I expected from a 60 euro VPS plan (from a provider in my county, due to project requirements for local peering) on a main node with 16 users over old dual Xeon's. I expected a big crap and I got close to a native-dedicated performance.
    As for Xen it's always has been slow for me when i decide to load it up with CPU-intensive stuff. Regardless of the type of the project, most of the times a VPS for around $30 is slower most of the time, compared to a crappy dedicated Pentium with same or close specs. But it has some advances - it's indeed more isolated. If I run a seedbox over Xen you can guess what happens. It seeds like crap if it ever seeds something. If I do this on a OpenVZ container the seedbox will seed with huge speeds and kill the performance of the node.

    Quote Originally Posted by cloudvps View Post
    Windows is the known limitation of OpenVZ, of course, if you plan to deploy Windows images OVZ is not for you.
    I would use WindowsOS host with Virtuozzo for that purpose.
    Also, from what I know, KVM has pretty good performance with Windows guests.
    I've tested KVM theese days. It runs great for Linuxes, but it's terrible for Windows! But it's somehow fairly, the box that i've tested it on crashed a lot (the hardware is not damaged). Now the same box runs EXSi for testing and no problems so far on my tests.

    I repeat the above is based on personal experience.
    Last edited by danceboysf; 03-08-2010 at 06:44 PM.

  25. #25
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    based on personal experience XEN is much better than OpenVZ.
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