FAQ

[CentOS-virt] moving from Xen to KVM

Dave Augustus
Feb 24, 2010 at 2:16 pm
Hello All,

I have been building a new server to deploy using Xen. However, seeing
that Redhat is moving towards KVM, it would seem beneficial to deply
this server using KVM as well. This is a Centos 5.4 x86_64 fresh
install.

So here is the scoop:

* running the xen kernel with 2 vms works great. I have 2 vms- a
cobbler host and an ldap host.
* running with non-xen kernel, I can't seem to get anything to
work right. Using virt-install from the command line, I get the
response of "Host does not support any virtualization options"
yet I know it does.


What am I missing here?

I spent some hours last night searching and came up empty.

Thanks in advance,
Dave
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14 responses

  • Adam at Feb 24, 2010 at 6:14 pm
    Did you install kvm?

    If you need to move the xen virtual machines to kvm you will need to boot
    them in rescue mode, change your modprobe.conf to load the regular scsci and
    nic drivers, install a regular kernel, remove the xen console from inittab
    and remove console=xvc0 from your /etc/grub.conf and reboot.

    -Adam

    On Wed, Feb 24, 2010 at 9:16 AM, Dave Augustus
    wrote:
    Hello All,

    I have been building a new server to deploy using Xen. However, seeing that
    Redhat is moving towards KVM, it would seem beneficial to deply this server
    using KVM as well. This is a Centos 5.4 x86_64 fresh install.

    So here is the scoop:

    - running the xen kernel with 2 vms works great. I have 2 vms- a
    cobbler host and an ldap host.
    - running with non-xen kernel, I can't seem to get anything to work
    right. Using virt-install from the command line, I get the response of "Host
    does not support any virtualization options" yet I know it does.


    What am I missing here?

    I spent some hours last night searching and came up empty.

    Thanks in advance,
    Dave

    _______________________________________________
    CentOS-virt mailing list
    CentOS-virt at centos.org
    http://lists.centos.org/mailman/listinfo/centos-virt
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  • Dave Augustus at Feb 24, 2010 at 11:14 pm
    What is needed to install kvm? I have the non xen kernel as the
    default. I have virsh, virt-install installed. What am I missing in my
    config? Look at my second bullet point to get a sense of where I am
    stuck.

    Thanks for your help,
    Dave
    On Feb 24, 2010, at 12:14 PM, Adam wrote:

    Did you install kvm?

    If you need to move the xen virtual machines to kvm you will need to
    boot them in rescue mode, change your modprobe.conf to load the
    regular scsci and nic drivers, install a regular kernel, remove the
    xen console from inittab and remove console=xvc0 from your /etc/
    grub.conf and reboot.

    -Adam

    On Wed, Feb 24, 2010 at 9:16 AM, Dave Augustus <davea at ingraftedsoftware.com
    wrote:
    Hello All,

    I have been building a new server to deploy using Xen. However,
    seeing that Redhat is moving towards KVM, it would seem beneficial
    to deply this server using KVM as well. This is a Centos 5.4 x86_64
    fresh install.

    So here is the scoop:
    running the xen kernel with 2 vms works great. I have 2 vms- a
    cobbler host and an ldap host.
    running with non-xen kernel, I can't seem to get anything to work
    right. Using virt-install from the command line, I get the response
    of "Host does not support any virtualization options" yet I know it
    does.

    What am I missing here?

    I spent some hours last night searching and came up empty.

    Thanks in advance,
    Dave

    _______________________________________________
    CentOS-virt mailing list
    CentOS-virt at centos.org
    http://lists.centos.org/mailman/listinfo/centos-virt


    _______________________________________________
    CentOS-virt mailing list
    CentOS-virt at centos.org
    http://lists.centos.org/mailman/listinfo/centos-virt
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  • Dennis J. at Feb 25, 2010 at 1:32 am
    Do you have the "kvm" package installed?
    Also what exactly do you mean by "KVM as well"? Are you aware that you can
    only run Xen or KVM but not both at the same time on the same host?

    Regards,
    Dennis
    On 02/25/2010 12:14 AM, Dave Augustus wrote:
    What is needed to install kvm? I have the non xen kernel as the default.
    I have virsh, virt-install installed. What am I missing in my config?
    Look at my second bullet point to get a sense of where I am stuck.

    Thanks for your help,
    Dave

    On Feb 24, 2010, at 12:14 PM, Adam <adam0x54 at gmail.com
    wrote:
    Did you install kvm?

    If you need to move the xen virtual machines to kvm you will need to
    boot them in rescue mode, change your modprobe.conf to load the
    regular scsci and nic drivers, install a regular kernel, remove the
    xen console from inittab and remove console=xvc0 from your
    /etc/grub.conf and reboot.

    -Adam

    On Wed, Feb 24, 2010 at 9:16 AM, Dave Augustus <
    <mailto:davea at ingraftedsoftware.com>davea at ingraftedsoftware.com
    wrote:

    Hello All,

    I have been building a new server to deploy using Xen. However,
    seeing that Redhat is moving towards KVM, it would seem beneficial
    to deply this server using KVM as well. This is a Centos 5.4
    x86_64 fresh install.

    So here is the scoop:

    * running the xen kernel with 2 vms works great. I have 2 vms-
    a cobbler host and an ldap host.
    * running with non-xen kernel, I can't seem to get anything to
    work right. Using virt-install from the command line, I get
    the response of "Host does not support any virtualization
    options" yet I know it does.


    What am I missing here?

    I spent some hours last night searching and came up empty.

    Thanks in advance,
    Dave

    _______________________________________________
    CentOS-virt mailing list
    <mailto:CentOS-virt at centos.org>CentOS-virt at centos.org
    <mailto:CentOS-virt at centos.org>
    <http://lists.centos.org/mailman/listinfo/centos-virt>http://lists.centos.org/mailman/listinfo/centos-virt


    _______________________________________________
    CentOS-virt mailing list
    CentOS-virt at centos.org <mailto:CentOS-virt at centos.org>
    http://lists.centos.org/mailman/listinfo/centos-virt

    _______________________________________________
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    http://lists.centos.org/mailman/listinfo/centos-virt
  • Dave Augustus at Feb 26, 2010 at 1:58 am
    Thanks for all the responses!!!

    I finally realized that when running Xen and in Dom0, Xen hides the
    AMD-V in /proc/cpuinfo

    (...more reasons to move to KVM)

    Now to convert my Xen vms to KVM.

    --
    Dave

    On Thu, 2010-02-25 at 02:32 +0100, Dennis J. wrote:

    Do you have the "kvm" package installed?
    Also what exactly do you mean by "KVM as well"? Are you aware that you can
    only run Xen or KVM but not both at the same time on the same host?

    Regards,
    Dennis
    On 02/25/2010 12:14 AM, Dave Augustus wrote:
    What is needed to install kvm? I have the non xen kernel as the default.
    I have virsh, virt-install installed. What am I missing in my config?
    Look at my second bullet point to get a sense of where I am stuck.

    Thanks for your help,
    Dave

    On Feb 24, 2010, at 12:14 PM, Adam <adam0x54 at gmail.com
    wrote:
    Did you install kvm?

    If you need to move the xen virtual machines to kvm you will need to
    boot them in rescue mode, change your modprobe.conf to load the
    regular scsci and nic drivers, install a regular kernel, remove the
    xen console from inittab and remove console=xvc0 from your
    /etc/grub.conf and reboot.

    -Adam

    On Wed, Feb 24, 2010 at 9:16 AM, Dave Augustus <
    <mailto:davea at ingraftedsoftware.com>davea at ingraftedsoftware.com
    wrote:

    Hello All,

    I have been building a new server to deploy using Xen. However,
    seeing that Redhat is moving towards KVM, it would seem beneficial
    to deply this server using KVM as well. This is a Centos 5.4
    x86_64 fresh install.

    So here is the scoop:

    * running the xen kernel with 2 vms works great. I have 2 vms-
    a cobbler host and an ldap host.
    * running with non-xen kernel, I can't seem to get anything to
    work right. Using virt-install from the command line, I get
    the response of "Host does not support any virtualization
    options" yet I know it does.


    What am I missing here?

    I spent some hours last night searching and came up empty.

    Thanks in advance,
    Dave

    _______________________________________________
    CentOS-virt mailing list
    <mailto:CentOS-virt at centos.org>CentOS-virt at centos.org
    <mailto:CentOS-virt at centos.org>
    <http://lists.centos.org/mailman/listinfo/centos-virt>http://lists.centos.org/mailman/listinfo/centos-virt


    _______________________________________________
    CentOS-virt mailing list
    CentOS-virt at centos.org <mailto:CentOS-virt at centos.org>
    http://lists.centos.org/mailman/listinfo/centos-virt

    _______________________________________________
    CentOS-virt mailing list
    CentOS-virt at centos.org
    http://lists.centos.org/mailman/listinfo/centos-virt
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  • Pasi Kärkkäinen at Feb 26, 2010 at 5:07 pm

    On Thu, Feb 25, 2010 at 07:58:04PM -0600, Dave Augustus wrote:
    Thanks for all the responses!!!

    I finally realized that when running Xen and in Dom0, Xen hides the AMD-V
    in /proc/cpuinfo
    Yes, because AMD-V is used by the Xen hypervisor. Dom0 is just a guest,
    so it doesn't see the AMD-V capability in /proc/cpuinfo.

    -- Pasi
  • Pasi Kärkkäinen at Feb 24, 2010 at 9:38 pm

    On Wed, Feb 24, 2010 at 08:16:53AM -0600, Dave Augustus wrote:
    Hello All,

    I have been building a new server to deploy using Xen. However, seeing
    that Redhat is moving towards KVM, it would seem beneficial to deply this
    server using KVM as well. This is a Centos 5.4 x86_64 fresh install.

    So here is the scoop:

    * running the xen kernel with 2 vms works great. I have 2 vms- a cobbler
    host and an ldap host.
    * running with non-xen kernel, I can't seem to get anything to work
    right. Using virt-install from the command line, I get the response of
    "Host does not support any virtualization options" yet I know it does.

    What am I missing here?

    I spent some hours last night searching and came up empty.
    What does "xm info" say about caps/capabilities?
    Do you see hvm supported?

    Xen HVM guests require CPU virtualization extensions (Intel VT, AMD-V) to be present
    and enabled in the BIOS.

    -- Pasi
  • Iain Morris at Feb 26, 2010 at 9:14 pm

    On Wed, Feb 24, 2010 at 1:38 PM, Pasi K?rkk?inen wrote:
    Xen HVM guests require CPU virtualization extensions
    ... snip ...
    and enabled in the BIOS.
    This seems obvious but has caught me before, wasting some time. Dell
    PowerEdge systems seem to ship with virt disabled in the bios.

    -Iain

    --
    -- -
    Iain Morris
    iain.t.morris at gmail.com
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  • Christopher G. Stach II at Feb 26, 2010 at 8:03 am

    ----- "Dave Augustus" wrote:

    I finally realized that when running Xen and in Dom0, Xen hides the
    AMD-V in /proc/cpuinfo
    Really?

    dom0:

    flags : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt lm 3dnowext 3dnow constant_tsc pni monitor cx16 lahf_lm cmp_legacy svm cr8_legacy

    guest:

    flags : fpu tsc msr pae mce cx8 apic mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt lm 3dnowext 3dnow constant_tsc pni monitor cx16 lahf_lm cmp_legacy svm cr8_legacy
    (...more reasons to move to KVM)
    I have a hunch that you are going to do whatever you are told to do and that you really have no idea what is going on.

    Can we get more "Hey, I'm told KVM is cool so I'm migrating all of my production servers to it because the free OS of my choice may not support it in a year or two after I leave my current suckjob position and I hear, since I don't read mainline kernel mailing lists religiously and keep only a superficial idea in my head about kernel development, since I really have no idea what 'kernel development' means, that KVM is the only Jesus-approved way of doing things" threads? None of you seem to have have a head for any of this, it seems.

    Maybe you're just working for Billy's Interwebs-r-Us and keeping Sally's Nail Shop going strong, but the last time I checked, the "ent" in CentOS stood for "enterprise".

    Here are a few tips:

    1. Fuck KVM.
    2. Stick with Xen because there is quite a lot of time until 5 is EOL'd and if you haven't noticed, it's actually a mature technology.
    3. Figure out what you are going to do with Sally's Nail Shop in the meantime. If you have time to fuck everything up in your environment with KVM, you can probably save 20% or more optimizing your environment and even more with proper capital investments and training.
    4. Figure out how either a) non-critical/enterprise services would ever be served by KVM's features or lack thereof, or b) you are going to CYA when you can't guarantee an SLA.
    5. Spend more time on KVM dev lists instead of posting here and annoying others with your butthurt KVM-won't-work posts, as it's not even supported upstream.

    --
    Christopher G. Stach II
    http://ldsys.net/~cgs/
  • Compdoc at Feb 26, 2010 at 3:26 pm
    KVM works. I'm happy with it. But then I build servers with
    6 guests or less for small businesses.

    There are comparisons. They say KVM doesn't scale as well.
    They say in some areas xen shines, and in some areas kvm
    shines. But the comparisons are all from last year before
    red hat released 5.4.

    RHEL 5.5, which includes many improvements will be out
    shortly. Think I'll stick with it...
  • Hildebrand, Nils, 232 at Mar 17, 2010 at 1:15 pm
    Hi,

    just two questions:
    1. Is there anything faster than XEN-paravirtualization?

    2. Why XEN 5?
    XEN 3 is quite stable, too.

    I have 31 DomUs up and running on a single Box - and have a strong feeling that even 60 will run flawless.
    But: All of them are Para-Virtualized.

    I have no problem with disk IO-Bottlenecks since my DomUs are not Database-Servers - so there is mostly static information in the filesystems.

    I see no reason why I should move to KVM.
    My only limitation is memory, since RAM is not being virtually mapped yet.


    Kind regards

    Nils

    -----Urspr?ngliche Nachricht-----
    Von: centos-virt-bounces at centos.org
    [mailto:centos-virt-bounces at centos.org] Im Auftrag von
    Christopher G. Stach II
    Gesendet: Freitag, 26. Februar 2010 09:04
    An: Discussion about the virtualization on CentOS
    Betreff: Re: [CentOS-virt] moving from Xen to KVM
    [...]
    Here are a few tips:

    1. F*** KVM.
    2. Stick with Xen because there is quite a lot of time until
    5 is EOL'd and if you haven't noticed, it's actually a mature
    technology. [...]
  • Dennis J. at Mar 17, 2010 at 1:35 pm

    On 03/17/2010 02:15 PM, Hildebrand, Nils, 232 wrote:
    Hi,

    just two questions:
    1. Is there anything faster than XEN-paravirtualization?

    2. Why XEN 5?
    XEN 3 is quite stable, too.

    I have 31 DomUs up and running on a single Box - and have a strong feeling that even 60 will run flawless.
    But: All of them are Para-Virtualized.

    I have no problem with disk IO-Bottlenecks since my DomUs are not Database-Servers - so there is mostly static information in the filesystems.
    The term "paravirtualization" is becoming quite dated. Even if you install
    a KVM guest without that option if you choose the virtio driver inside then
    you still end up with "paravirtualized" I/O. With the advent of things like
    nested page tables and SR-IOV the "fully virtualized=slow,
    paravirtualized=way faster" logic is no longer necessarily true at least
    not for every aspect of the system.

    Regards,
    Dennis

    (Disclaimer: So far I'm running all my virtualized servers on Xen but use
    KVM exclusively at home. Eventually I plan to migrate to KVM on the servers
    too but at the moment I'm not in a hurry but that is not because i think
    KVM isn't up for the task but because there is no urgent need to do so.)
  • Grant McWilliams at Mar 17, 2010 at 10:49 pm

    On Wed, Mar 17, 2010 at 6:35 AM, Dennis J. wrote:
    On 03/17/2010 02:15 PM, Hildebrand, Nils, 232 wrote:
    Hi,
    I have 31 DomUs up and running on a single Box - and have a strong
    feeling that even 60 will run flawless.
    But: All of them are Para-Virtualized.

    I have no problem with disk IO-Bottlenecks since my DomUs are not
    Database-Servers - so there is mostly static information in the filesystems.

    The term "paravirtualization" is becoming quite dated. Even if you install
    a KVM guest without that option if you choose the virtio driver inside then
    you still end up with "paravirtualized" I/O. With the advent of things like
    nested page tables and SR-IOV the "fully virtualized=slow,
    paravirtualized=way faster" logic is no longer necessarily true at least
    not for every aspect of the system.

    Regards,
    Dennis
    In the Xen world paravirtualizing will be replaced by Hybrid virtualizing.
    As hardware virt becomes faster (ie, not so slow) then Xen will change to
    using HVM as the default and paravirtualize EVERYTHING else. This is not the
    same thing as KVM which uses hardware virt for cpu, emulation for most
    things except disk and network which are paravirtualized (if chosen). I look
    forward to this as HVM in Xen is slower than KVM even though it's kind of
    doing the same thing. However, I don't think people have benchmarked either
    enough to realize how much of a hit we're taking with virtio.

    KVM has some neat tricks up their sleeve as well like shared memory, nesting
    etc.. I may put up a KVM box just because I need nesting (for a classroom to
    teach virtualization).

    Grant McWilliams

    Some people, when confronted with a problem, think "I know, I'll use
    Windows."
    Now they have two problems.
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  • Pasi Kärkkäinen at Mar 18, 2010 at 7:34 pm

    On Wed, Mar 17, 2010 at 03:49:40PM -0700, Grant McWilliams wrote:
    On Wed, Mar 17, 2010 at 6:35 AM, Dennis J. wrote:
    On 03/17/2010 02:15 PM, Hildebrand, Nils, 232 wrote:
    Hi,
    I have 31 DomUs up and running on a single Box - and have a strong
    feeling that even 60 will run flawless.
    But: All of them are Para-Virtualized.

    I have no problem with disk IO-Bottlenecks since my DomUs are not
    Database-Servers - so there is mostly static information in the
    filesystems.

    The term "paravirtualization" is becoming quite dated. Even if you
    install
    a KVM guest without that option if you choose the virtio driver inside
    then
    you still end up with "paravirtualized" I/O. With the advent of things
    like
    nested page tables and SR-IOV the "fully virtualized=slow,
    paravirtualized=way faster" logic is no longer necessarily true at least
    not for every aspect of the system.

    Regards,
    ? Dennis

    In the Xen world paravirtualizing will be replaced by Hybrid virtualizing.
    As hardware virt becomes faster (ie, not so slow) then Xen will change to
    using HVM as the default and paravirtualize EVERYTHING else. This is not
    the same thing as KVM which uses hardware virt for cpu, emulation for most
    things except disk and network which are paravirtualized (if chosen). I
    look forward to this as HVM in Xen is slower than KVM even though it's
    kind of doing the same thing.? However, I don't think people have
    benchmarked either enough to realize how much of a hit we're taking with
    virtio.
    Do you have some benchmarks showing Xen HVM is slower than KVM?
    I believe so far Xen HVM has actually been faster than KVM.
    KVM has some neat tricks up their sleeve as well like shared memory,
    nesting etc.. I may put up a KVM box just because I need nesting (for a
    classroom to teach virtualization).
    Lately Xen has gotten a couple of different types of memory sharing implementations aswell.
    At least one of them will ship in upcoming Xen 4.0.0.

    -- Pasi
    Grant McWilliams

    Some people, when confronted with a problem, think "I know, I'll use
    Windows."
    Now they have two problems.

    References

    Visible links
    1. mailto:dennisml at conversis.de
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  • Pasi Kärkkäinen at Mar 17, 2010 at 2:16 pm

    On Wed, Mar 17, 2010 at 02:15:52PM +0100, Hildebrand, Nils, 232 wrote:
    Hi,

    just two questions:
    1. Is there anything faster than XEN-paravirtualization?

    2. Why XEN 5?
    XEN 3 is quite stable, too.
    I guess you mean Citrix XenServer 5.5 with "Xen 5" ?

    It's a completely different, full commercially supported product from Citrix,
    which has the opensource Xen hypervisor as a part of it. Actually it's based on CentOS.

    Citrix XenServer 5.x uses Xen 3.x hypervisor.
    I have 31 DomUs up and running on a single Box - and have a strong feeling that even 60 will run flawless.
    But: All of them are Para-Virtualized.
    Yeah, Linux PV guests perform and work OK.

    -- Pasi
    I have no problem with disk IO-Bottlenecks since my DomUs are not Database-Servers - so there is mostly static information in the filesystems.

    I see no reason why I should move to KVM.
    My only limitation is memory, since RAM is not being virtually mapped yet.


    Kind regards

    Nils

    -----Urspr?ngliche Nachricht-----
    Von: centos-virt-bounces at centos.org
    [mailto:centos-virt-bounces at centos.org] Im Auftrag von
    Christopher G. Stach II
    Gesendet: Freitag, 26. Februar 2010 09:04
    An: Discussion about the virtualization on CentOS
    Betreff: Re: [CentOS-virt] moving from Xen to KVM
    [...]
    Here are a few tips:

    1. F*** KVM.
    2. Stick with Xen because there is quite a lot of time until
    5 is EOL'd and if you haven't noticed, it's actually a mature
    technology. [...]
    _______________________________________________
    CentOS-virt mailing list
    CentOS-virt at centos.org
    http://lists.centos.org/mailman/listinfo/centos-virt

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