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Does XEN counts Dedicated and Swap Memory?
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Does XEN counts Dedicated and Swap Memory?

Hello,
I have a question. If I create VPS on a XEN Virtualized Dedicated Server.

XEN does not allow Overselling of nodes same as KVM.

Does it counts the Swap to be dedicated too or Only the Allocated RAM.

Eg. My dedicated is 32GB Ram.
I am selling 256MB VPS with Swap 256MB.

So 32gb/256mb = 128 VPS
Or
32gb/512mb (swap and allocated) = 64 VPS

Thanks

Comments

  • Xen and kvm allows overselling. Get over the myths :)

    Thanked by 1tux
  • MaouniqueMaounique Host Rep, Veteran

    Swap on Xen/KVM is on disk on special partition on the virtual disk. The memory is memory, swap is disk same as any other physical machine.

  • @Maounique said:
    Swap on Xen/KVM is on disk on special partition on the virtual disk. The memory is memory, swap is disk same as any other physical machine.

    So it means i can sell 128 VPS with 256 mb ram and 256mb swap with 32 gb ram dedicated

  • @concerto49 said:
    Xen and kvm allows overselling. Get over the myths :)

    I think they dont allow overselling memory.
    Do they?

  • @mazker said:
    Do they?

    They do

  • So why does most people like to buy XEN/KVM VPS and Not OpenVZ? Anything special?

  • MaouniqueMaounique Host Rep, Veteran

    @mazker said:
    So why does most people like to buy XEN/KVM VPS and Not OpenVZ? Anything special?

    Well, it is harder to oversell memory, but the main reason people think Xen/KVM are not possible to oversell is that the kiddie hosts cant do it and most offers with those are offering good performance.
    There are tons of good OVZ providers out there that sell good OVZ with same performances as Xen/KVM for cheaper.

  • mazker said: So why does most people like to buy XEN/KVM VPS and Not OpenVZ? Anything special?

    Lack of updated knowledge. It used to be the case before balloon memory was introduced way back when dinosaurs walked the earth (2008?)

    That said, the CPU scheduler might be another thing that pushes people towards/away from XEN at least.

  • Does XEN also allow Overselling the RAM?

  • MaouniqueMaounique Host Rep, Veteran

    Yes.

  • AnthonySmithAnthonySmith Member, Patron Provider

    LOL this old nugget

    @OP you need to keep some ram dedicated to your Xen Hypervisor, the rest you can sell, Swap is disk based so does not affect Ram.

    @bollocks_talkers give me a working functional example of Ram overselling on Xen in a hosting environment, tip: ballooning is not overselling or even over allocating.

  • MaouniqueMaounique Host Rep, Veteran
    edited November 2013

    @AnthonySmith said:
    ballooning is not overselling or even over allocating.

    Yes and no. Technically OVZ cannot use more than the allocated ram either, if most people use it to the brink, various catastrophic events happen.
    Ballooning and thin provisioning can work on Xen. They do degrade performance, true, but can be well managed, Digital Ocean uses thin provisioning and the disks are not crawling, AFAIK, it might be SSD and KVM but the principle is similar.
    Overselling can happen on xen in some conditions whether you like to admit it or not.
    Now I do not say you or anyone else is doing it, but it is possible and if a host wants to do it and has average technical knowledge, it can with good results.
    On the other hand OVZ needs really good disks and CPU while xen forces a lower density on a server so disks and CPU can be less expensive and they are more than half of the price of a server, RAM is not everything.
    As a host I would choose to do only Xen/KVM, cheaper hardware, better prices, less abuse of resources and even if it is, better isolation, happier customers, higher return per customer and less variable costs with support, chargebacks and fees to paypal, etc, happier host. Dont play the victim of OVZ RAM race and unscrupulous hosts here, it does not become you.

  • AnthonySmithAnthonySmith Member, Patron Provider

    once again, no one ever gives a working example for a hosting environment.. sorry it just cant be done, it is not a case of admitting anything or not liking it, frankly I cannot wait for them to lift the hard limited design which is coming soon.

    It is not a yes and no answer, ballooning is not over allocating, it is taking from A and lending temporarily to B in the full view and knowledge of A, at best ballooning is memory management and sharing for private use.

  • MaouniqueMaounique Host Rep, Veteran
    edited November 2013

    OK, admitting it is so and RAM cannot be practically overallocated (I think it can be, not everyone is disabling it but I concede this point to you), still disk can. Thin provisioning does work pretty well, especially on SSD and I did it many times (at work and home, not for prometeus, of course).
    As for the CPU, you cant run 384 GB ram OVZ servers, it is practically impossible due to CPU limitations. If you add 512 RAM to a server which copes with 384 on OVZ and run Xen on it, you can sell almost the same number of VMs at higher price and get more money while possibly investing less in disks.

  • Maounique said: As for the CPU, you cant run 384 GB ram OVZ servers, it is practically impossible due to CPU limitations.

    If I'm not mistaken, @serverian uses 384 GB RAM OVZ servers for vpsdime.

  • @dhamaniasad said:
    If I'm not mistaken, serverian uses 384 GB RAM OVZ servers for vpsdime.

    he's talking about that the cpu will be the bottleneck when you have such a high RAM OVZ server

  • MaouniqueMaounique Host Rep, Veteran

    It can work for very high ram VPSes. But almost everyone who does this (high ram OVZ), if I am not mistaken, has to put limits on CPU usage, nobody allows full load as we do. In normal conditions if people were allowed to use the cores advertised, it would not work.

  • AnthonySmithAnthonySmith Member, Patron Provider

    oh yeah, disk can be, but its so damn cheap why bother :)

  • MaouniqueMaounique Host Rep, Veteran
    edited November 2013

    @AnthonySmith said:
    oh yeah, disk can be, but its so damn cheap why bother :)

    I dont think so, 600 GB SAS 10k short stroke disks cost about the same as a SSD, for instance.
    For cheap SATA, yeah, I agree, but people like SSD more and overselling there works better because it is so much faster at seek.

  • If you're planning on KVM overcommit, take a look at some KVM tools like: Kernel Same-page Merging (KSM). – Memory ballooning, and – Thin storage provisioning.

  • AnthonySmithAnthonySmith Member, Patron Provider

    @Maounique said:
    For cheap SATA, yeah, I agree, but people like SSD more and overselling there works better because it is so much faster at seek.

    I would take SSD cached SATA over straight SAS to begin with but I suppose the bottom line is that cheap is a matter of opinion and mine is that these days storage + performance is cheap these days.

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