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  1. #1
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    OpenVZ vs Xen: as a customer, which would you prefer?

    I know that there probably have been other threads like this, but I had a more specific question in mind that gets rid of some of the most common comments on this kind of topic.

    Let's assume that you know this:
    • All other specifications of the box (i.e. configuration, number of VMs per server, etc.) are kept constant.
    • The box is not oversold.
    • They are offered at the same price.
    • The box is stable.
    • The OpenVZ VPS does not have burst RAM.

    As a customer, which would you prefer to purchase and why?

  2. #2
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  3. #3
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    Xen xen xen xen XEN!

    Ability to run my own kernel, load my own modules, get console access, etc, etc.

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  5. #5
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    same price, xen then, but thats very unlikely to happen.

    main reason, memory issues with openvz, because you have swap with xen, and it wont freaks out at times it gets to use whole RAM, and openvz is going to, start killing processes and eventually be dead/unusable.

  6. #6
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    Xen

    Why? Linux or Windows, and most importantly, it's a real "Virtual Machine."

  7. #7
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    As with everyone else here so far, Xen.

    Why? Because I can run my own kernel, load my own modules, get console access, and so on.

    If I had the choice between choosing between two well established providers (one OpenVZ, the other Xen) with plans that are the same specs, and cost the same amount - I would always go with the Xen provider - it's just more like having a dedicated server that way, and you won't have to pester your host to change your /proc/user_beancounters, if needed etc.

    Having said that, all the VPS providers I currently use are OpenVZ based, and I generally am happy with OpenVZ VPS too.
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  8. #8
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    Xen all the way!
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  9. #9
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    If at the same price point, it wouldn't matter to me ... the average end-user. For webmasters/techs, I know would prefer Xen for kernal and/or module adjustments. My current server config uses OpenVZ and I have no problems issues with using it.

  10. #10
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    I believe with everything else equal Xen will give better stability while OpenVZ will offer better performance. Xen also offers features (eg. custom kernel) that OpenVZ can't. So I might choose either depending on the needs of the project - special requirements vs speed vs risk. Based on past experience I've had best results on Virtuozzo, but that's probably more down to the providers than the technology.

    However:
    Quote Originally Posted by InsDel View Post
    [*]The OpenVZ VPS does not have burst RAM.
    On UBC, burst memory is an absolute requirement - around double the "guaranteed" is normal. If there's no burst (ie. burst is set equal to guaranteed) I'll assume that your plan offers half its nominal memory.
    Last edited by foobic; 12-17-2009 at 06:13 PM.
    Chris

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  11. #11
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    I'm with foobic, depending on my needs. Xen has some really nice features that can make or break the decision but only if you need those features and not everyone does. I know most people say Xen is more stable and that may be true but in all honesty having both OpenVZ and Xen accounts for a long time I haven't see any difference in stability (comparing same level of quality host).

  12. #12
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    Okay then - will anybody's opinion change if the OpenVZ has the common burst RAM of twice the 'guaranteed' amount?

  13. #13
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    Quote Originally Posted by InsDel View Post
    Okay then - will anybody's opinion change if the OpenVZ has the common burst RAM of twice the 'guaranteed' amount?
    For me? No, because its not "true" virtualization. As far as I'm concerned, it's just glorified shared hosting. Yes it's a bit more than that, but that's the feeling I get from it.

  14. #14
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    Quote Originally Posted by InsDel View Post
    Okay then - will anybody's opinion change if the OpenVZ has the common burst RAM of twice the 'guaranteed' amount?
    I doubt it - that's just the standard setup for OpenVZ (and necessary to get something comparable to a Xen VPS of the same nominal memory). Don't believe the hype about "burst" RAM.
    Last edited by foobic; 12-17-2009 at 06:57 PM. Reason: additional
    Chris

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  15. #15
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    Quote Originally Posted by InsDel View Post
    Okay then - will anybody's opinion change if the OpenVZ has the common burst RAM of twice the 'guaranteed' amount?
    Nope, would still rather have the Xen VPS. "Burst" RAM while sounding good in theory, is not in reality.
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  16. #16
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    Xen is my choice :0)

  17. #17
    Quote Originally Posted by InsDel View Post
    Okay then - will anybody's opinion change if the OpenVZ has the common burst RAM of twice the 'guaranteed' amount?
    If OpenVZ has xMB "guaranteed" RAM, and burstable to 3*x MB RAM, it means that if the host is not heavily loaded, It is possible for you to use up to 3*x MB RAM in total.
    If Xen has xMB RAM, and 2*MB swap on disk, I will take Xen. Though part of it might be swap, Xen can always use all its specified memory, while you may not always be able to burst to the limit under OpenVZ.
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    Last edited by whzcjint; 12-17-2009 at 09:05 PM.

  18. #18
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    I never consider "burst ram" in my decision, never count on it and never expect to have it. That said I've chosen OpenVZ almost as often as Xen.

  19. #19
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    Quote Originally Posted by whzcjint View Post
    If OpenVZ has xMB "guaranteed" RAM, and burstable to 3*x MB RAM, it means that if the host is not heavily loaded, It is possible for you to use up to 3*x MB RAM in total.
    No, it's not (possible for you to use up to 3*x MB RAM). This is the myth about burst RAM. The reality is:
    • You're constantly being monitored on two (actually more than two, but let's keep it simple) measures: One called "burst", the other called "guaranteed", both misnamed.
    • Memory actually used corresponds roughly to the guaranteed measurement.
    • Memory usage shown in top and free corresponds to the burst measurement.
    • The burst measurement is always higher than the guaranteed, sometimes considerably so, depending on the programs you're running. For the sake of argument, say it's double.
    • So if you ever want to be able to actually use as much memory as your guaranteed limit you need the burst limit to be double - and then you'll hit both limits at the same time.

    UBC is a very weird system, but none of this is a problem as long as the provider knows what they're doing. Unfortunately you can't always rely on this being the case.
    Chris

    "Some problems are so complex that you have to be highly intelligent and well informed just to be undecided about them." - Laurence J. Peter

  20. #20
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    Xen. It offers true virtualization and better security.

  21. #21
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    Quote Originally Posted by foobic View Post
    • Memory actually used corresponds roughly to the guaranteed measurement.
    • Memory usage shown in top and free corresponds to the burst measurement.
    So if I run 'ps aux' on my box, the 'guaranteed' measurement corresponds to RSS, while the 'burst' measurement corresponds to VSZ?

  22. #22
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    Good question. I've only looked at top / free against /proc/user_beancounters. VZ machines used to show the memory figures for the entire node there, but more recent versions fake the figures from either privvmpages (UBC "burst") or SLM memory. I'll go and do some adding up on RSS / VSZ...
    Chris

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  23. #23
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    Ok, for interest, on an almost idle OpenVZ box (512MB guaranteed, 1024MB burst):
    oomguarpages held: 8467 = 33MB usage against "guaranteed"
    privvmpages held: 54619 = 213MB usage against "burst"
    free -m shows: total 1024MB used 213MB

    So free -m display simply represents privvmpages held, as expected.

    And from ps aux, adding all processes usage:
    Total VSZ: 376772 = 368MB
    Total RSS: 66832 = 65MB

    No idea what that means, except that RSS and VSZ don't seem to correspond to OpenVZ's measures. Unless I have something wrong, which is entirely possible. Any OpenVZ experts want to comment on this?
    Chris

    "Some problems are so complex that you have to be highly intelligent and well informed just to be undecided about them." - Laurence J. Peter

  24. #24
    I think Xen is best compared to the competitive technologies when its comes to performance.
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  25. #25
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    So, after some echo `ps aux | cut -c33-37 | sed "s/ //g" | sed 1d | tr '\n' '+' | sed "s/+$//"` | bc (forgive my horrible attempt at shell commands) on my 128MB guaranteed/256MB burst box while comparing it to my UBC, my RSS is consistently about 3MB above my oomguarpages (57MB/54MB).

    Also @keserhosting, I think the extra overhead involved in truer virtualization would slow down the VM slightly compared to OpenVZ (since it shares kernels/etc.).

  26. #26
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    Quote Originally Posted by InsDel View Post
    So if I run 'ps aux' on my box, the 'guaranteed' measurement corresponds to RSS, while the 'burst' measurement corresponds to VSZ?
    Not necessarily. Memory accounting on Linux is actually quite a complex matter. OpenVZ's user bean counters tried to simplify it for each VE, but at the end it is not really doing an optimal job...

    VSZ is the virtual memory size of your process -- that includes the memory that has been allocated, process/thread stack, shared library etc. It's closely related to privvmpages (allocated pages) but the readings from `ps aux` is not that accurate due to shared libraries.

    RSS is the residential memory, i.e. the actual physical memory used by this process. It should be corresponding to the held amount in oomguarpages in a non-overselling/non-swapping scenario. I think if your process gets swapped out on the physical server, RSS will reduce, but oomguarpages will actually stay the same (which is when your physpages is different from oomguarpages).

    And although beancounters are tracking two metrics (privvmpages/guaranteed and oomguarpages/burstable), I think there is really pointless to track the GUARANTEED memory due to the ability to swap on the host node. The "guaranteed" amount there is only to guarantee that your processes will not be killed during an OOM event. It can go above the barrier amount as long as the server does not run out of memory (OOM). HOWEVER, in order to reach an OOM event on a Linux server, you usually have to exhaust all the physical memory AND all the swap -- which by then the whole server will be extremely slow anyway and your processes are about as good as dead...

    Therefore -- just worry about the burstable memory Remember that's the amount your processes "allocated" rather than "used". So for programs doing slab allocation can usually kill the whole system as they allocate a lot more than they use (i.e. Java). Multi-threaded apps also use a lot more memory on OpenVZ as each thread has default 8MB stack on Linux, which again is allocated but rarely used.

    Yeah. Pick Xen or KVM if you can.

  27. #27
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    Everyone is choosing Xen Is there anyone out there who wants to use OpenVZ?
    Learning...

  28. #28
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    Xen

  29. #29
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    Xeeeeeeeeen!!!

    Although OpenVZ could be alright for a temp VPS (for testing or something) as it's cheap.

  30. #30
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    It depends how you intend to you the VPS both system has their own advantages and disadvantages, but i assuming i can only keep one for my own use i'll prefer Xen VPS.
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  31. #31
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    Xen for me

  32. #32
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    +1 for xen
    - do it your self.

  33. #33
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    Seems most admins here want XEN, why openvz are the majority is WHT VPS offers?

  34. #34
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    Cool

    Quote Originally Posted by NelsonT View Post
    Seems most admins here want XEN, why openvz are the majority is WHT VPS offers?
    Because it is cheaper and easier to oversell I guess :8
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  35. #35
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    Quote Originally Posted by jamjam View Post
    Because it is cheaper and easier to oversell I guess :8
    Cheaper how? They're both free. Easier to oversell, definitely, but then overselling isn't necessarily a problem in itself. Overloading and mismanagement will cause problems on any platform.

    OpenVZ is more like shared hosting in its resource allocations so it can give hosts more profit and give users more bang-per-buck. Check the benchmarks thread if you don't believe this. The major downside (as with shared hosting) is the risk of another user taking too much of the shared resource pool and affecting other VPSs. The solution (as with shared hosting) is good management / monitoring by the provider.

    Another quite separate issue with OpenVZ is the arcane UBC memory management that hardly any users seem to understand, so they may end up getting less than they expect. Then again, if they're expecting something equivalent to a dedicated server for $5 per month they're going to be disappointed anyway...

    Shared hosting - OpenVZ - Xen/KVM etc. all have their place. Users can choose whatever suits their needs.
    Chris

    "Some problems are so complex that you have to be highly intelligent and well informed just to be undecided about them." - Laurence J. Peter

  36. #36
    Greetings:

    Xen and VMWare over OpenVZ; all three are free.

    Thank you.
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  37. #37
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    Free VMware version is not for selling, is it?

    Quote Originally Posted by dynamicnet View Post
    Xen and VMWare over OpenVZ; all three are free.

  38. #38
    Greetings:

    It all comes down to packaging.

    Thank you.
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  39. #39
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    Virtuozzo has alot less overheads compared to XEN.
    IMHO, for most applications, Virtuozzo would deliver better performance.

    How many clients want to install their own kernel or configure a SWAP?
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  40. #40
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    Quote Originally Posted by dynamicnet View Post
    Greetings:

    It all comes down to packaging.

    Thank you.
    Perhaps some details?

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