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KVM or Xen HVM - which is better for this...?
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KVM or Xen HVM - which is better for this...?

I heard OpenVZ PV (para-virtualization) runs well and with very little (<=5%) overhead inside KVM. How about inside Xen HVM - has anyone tried that?

Looking for a versatile solution that will support different kinds of PV's (OpenVM, LXC and, ideally, also Xen PV). I should think Xen HVM would be better suited to this, but have not come across any hands-on reports about running PV's inside Xen HVM...

Comments

  • @DewlanceVPS Maybe know.

  • KVM is better, hands down. It just works.

    Thanked by 1aglodek
  • aglodekaglodek Member
    edited November 2013

    @petem said: KVM is better, hands down. It just works.

    Thanks, this I know. Tried myself, but not Xen HVM. Have you tried this with both? And what issues, if any, in this respect with Xen HVM..?

  • aglodek said: Thanks, this I know. Tried myself, but not Xen HVM. Have you tried this with both? And what issues, if any, in this respect with Xen HVM..?

    Yes I have. That's actually why I started kvm.sh, because I've found KVM to be easier to work with for both customers and administrators. The main issue is drivers, compatibility with all guest operating systems and so on. Sometimes ISOs won't even boot with Xen HVM. I like Xen PV, but not HVM. Can we just say that I'm biased towards KVM and leave it at that :P ?

    Thanked by 1aglodek
  • nonubynonuby Member
    edited November 2013

    OpenVZ is container virtualization, not para-virtual. In terms of nesting containers on pv/hvm guests, Heroku very successfully runs hundreds of lightweight containers (via LXC) inside Xen PV guests on AWS. Future version of openvz (or possibly now) use cgroups and namespaces which is pretty much what LXC does, so I guess it would be possible.

    Maybe check out docker.io if exploring lightweight container isolation..

    Thanked by 1aglodek
  • @nonuby said:
    OpenVZ is container virtualization, not para-virtual. In terms of nesting containers on pv/hvm guests, Heroku very successfully runs hundreds of lightweight containers (via LXC) inside Xen PV guests on AWS.

    Interesting. Just to be sure: inside Xen PV, not inside Xen HVM..??

    Maybe check out docker.io if exploring lightweight container isolation..

    Yes, I'm looking into that as well. Seems Docker.io uses LXC containers.

  • @petem said: (...) Can we just say that I'm biased towards KVM and leave it at that :P ?

    Same here ;) But took my bias hat off today to do some due diligence, just to be sure ;)

  • MaouniqueMaounique Host Rep, Veteran

    Xen HVM can do the same as KVM does, it is actively developed to reduce the overhead as much as possible, the goal being full virtualization benefits at paravirtualization speeds.
    It should be stable soon.
    Until then, KVM has better support in terms of drivers and stuff, but the speed is almost the same.

    Thanked by 1aglodek
  • smansman Member
    edited November 2013

    Maybe this is a stupid question but why would you want to run OpenVZ inside a VM? Wouldn't it run like crap? Also I'm assuming if you are the end user that your provider wouldn't be too happy about the load you are causing.

  • MaouniqueMaounique Host Rep, Veteran

    Actually no and it is for testing only, probably.
    The nodes that run OVZ are runing maybe hundreds of VMs and, of course, the load is big on cpu and disks but in a kvm will probably run much less, just 2-3 to test.
    IIRC BuyVM run OVZ inside KVM for a while, or maybe was Xen dont remember well.

  • aglodekaglodek Member
    edited November 2013

    @sman said: Maybe this is a stupid question but why would you want to run OpenVZ inside a VM? Wouldn't it run like crap? Also I'm assuming if you are the end user that your provider wouldn't be too happy about the load you are causing.

    (1) Why run OpenVZ inside a VM:

    • to have full control of the node with OpenVZ containers. OpenVZ has some very cool features, regrettably some of the most useful of them are not available to clients (from inside the containers). For example: backup/cloning/migration of entire containers.

    • distribute apps between containers. For example: offloaded Percona DB running in one container, supporting applications in 2-3 other containers, instead of multiple instances running in each container.

    • as @Maounique correctly surmised, for testing.

    (2) I have it on good authority that OpenVZ overhead adds about 5%. Another words, negligible :)

    (3) Your assumption is incorrect. Informed providers take no issue (I always make sure before ordering). Practically same load running apps all on one KVM or distributed between 2-4 OpenVZ containers on that same KVM. And sometimes less load (see Percona DB example in (1) above ;)

    Thanked by 1smallet
  • smansman Member
    edited November 2013

    @aglodek said:

    Those are just OpenVZ virtualization vs something else reasons. Why not just install OpenVZ on a Dedi then?

    If the issue is price why not just say so instead of pretending it's something else.

    If it's for testing just use ProxMox on a Dedi which can do both KVM and OpenVZ.

  • aglodekaglodek Member
    edited November 2013

    @sman: who's pretending? Sure, thanks for reminding me that cost is one more reason to do things on a $10 4GB KVM as opposed to a similar specs $20 dedi. Why piss away money? Better to spend it on a second 4GB KVM in another location or even two :) Frankly, though, the meager savings would be item (4) on my list above ;) By far more important is the flexibility and ease of installation/re-installation on a KVM as opposed to a dedi.

    EDIT: sorry, that's not a fair comparison. The $10 4GB KVM comes with RAID 10 HDD or even SDD. A comparable dedi with multiple disks and hardware RAID would set me back $80 or more! I was comparing to my test dedi with 1x HDD and no RAID, of course not suitable for any production use. So, yeah, you're right - price is a BIG issue! Looking at the many other advantages I hadn't realized ;)

    In fact I also run Proxmox on a dedi with both KVM and OpenVZ containers. And some other stuff INSIDE those KVM's that Proxmox can't do :) That's one location in the US, however, that doesn't begin to cover the 20+ locations worldwide that I have need for. That's where OpenVZ containers (and likely others) inside KVM's come into play :)

    Running OpenVZ inside KVM's insulates very nicely from hardware issues. While playing around with one or even two dedis is manageable, educational and very useful, expanding into 20+ locations worldwide carries with it a couple of new layers of complexity. Thanks but no thanks ;)

  • DewlanceVPSDewlanceVPS Member, Patron Provider

    With KVM you can oversell RAM(Eg: $10/m - 8GB RAM), XenPV/XenHVM is stable and business users preferred Xen.

  • MaouniqueMaounique Host Rep, Veteran

    Yes, running it in a VM is great for testing, is cheaper and has better performance than a dedi, it may even come with backups and other cool features.

  • @Maounique said: Yes, running it in a VM is great for testing (...)

    Actually, some people use it in production, and quite successfully at that, it seems...

    http://lowendtalk.com/discussion/10913/ginernet-16-99-year-ssd-openvz-512-mb-of-ram-512-of-vswap-and-30-lifetime-discount

    http://lowendtalk.com/discussion/7977/openvz-inside-kvm

  • MaouniqueMaounique Host Rep, Veteran

    Yes, as I said BuyVM used it at some point in time.

  • aglodekaglodek Member
    edited November 2013

    @DewlanceVPS said: With KVM you can oversell RAM(Eg: $10/m - 8GB RAM), XenPV/XenHVM is stable and business users preferred Xen.

    So I've heard. However, the question here is: how good Xen HVM is for running OpenVZ containers and maybe Xen PV inside it (as opposed to running things inside KVM)?

  • MaouniqueMaounique Host Rep, Veteran
    edited November 2013

    The PV kernel needs the xen stuff to work.
    I do not know if the OVZ kernel has it because was not designed with that in mind and they could have removed it, it is possible to be added if not present, but it is already very fragile and superpatched, it breaks by itself at times, I do not recommend making any changes, but, yeah, in theory, it should work, but it will be tedious and not worth it for testing purposes, only for production due to performance gain and I strongly recommend against that unless you know what you are doing in detail.
    Go with KVM, save a lot of headache.

    Thanked by 1aglodek
  • @Maounique said:
    I do not know if the OVZ kernel has it because was not designed with that in mind and they could have removed it [...]

    OpenVZ for RHEL6 has Xen-PV compatibility built in. OpenVZ for RHEL5 I think you need to use the -xen build to work in Xen-PV, but I've never tried that. It comes in handy for software testing, although I don't quite see the point in using it in a production environment.

  • MaouniqueMaounique Host Rep, Veteran

    Rallias said: OpenVZ for RHEL6 has Xen-PV compatibility built in.

    Well, I couldnt boot it in my testing environment, got kernel panics all the time while non-ovz centos 6 was working. Tried with newer and older, but maybe was something wrong in my setup. This happened some 6 months ago, perhaps 8.

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