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From Marcus Sorensen <>
Subject Re: QEMU support in CloudStack
Date Fri, 08 Feb 2013 15:22:43 GMT
On Feb 8, 2013 2:34 AM, "Dave Cahill" <> wrote:
> Hi,
> Recently I encountered two "nested virtualization" use cases which made me
> want QEMU hypervisor support in CloudStack. I'm interested to hear if
> anyone else is interested in this feature, and any notes on how it should
> be implemented.
> Here is a good explanation from OpenStack docs [2] on why they support
> "From the perspective of the Compute service, the QEMU hypervisor is very
> similar to the KVM hypervisor. Both are controlled through libvirt, both
> support the same feature set, and all virtual machine images that are
> compatible with KVM are also compatible with QEMU. The main difference is
> that QEMU does not support native virtualization. Consequently, QEMU has
> worse performance than KVM and is a poor choice for a production
> deployment."
> Here are the use cases I encountered:
> [Use case: Dev environment]
>     Wanted to use Vagrant [1] to create a portable multi-node dev
> environment; however Vagrant uses VirtualBox, which doesn't support KVM.
>     Also, devcloud uses VirtualBox and devcloud-kvm uses kvm-within-kvm. I
> imagine maintenance of devcloud and devcloud-kvm would be easier if
> devcloud-kvm could use VirtualBox too.

As a side note, I actually went the other way. If you look at the devcloud
docs, you'll see that you can now run devcloud and devcloud-kvm together,
not in virtual box, but under qemu-kvm.

>     Note: Of course, I'm aware of devcloud-kvm as an alternative for this
> use case, and I'll be looking into that next.
> [Use case: Demo environment]
>     We may want to spin up a multi-node CloudStack install in Amazon AWS
> for demo purposes.
>     Again, AWS instances don't support KVM, so this is not possible
> QEMU support.
> [Implementation ideas]
>     The management server currently does a check for KVM support
> on the host, and refuses to add the host if that fails. I think this check
> could be removed, as the agent setup scripts will fail anyway if the user
> is trying to setup a certain hypervisor on a machine which doesn't support
> it.
>     Create a new setting in like "use_qemu", with a
> default of "false". If the person deploying CloudStack agent sets this to
> "true", cloud-setup-agent and other setup scripts would ignore lack of KVM
> support as long as QEMU support was available.
>     Lastly, when creating the libvirt XML file for a VM, set hypervisor to
> QEMU rather than KVM in the XML file depending on the config setting.
> Thanks for reading,
> Dave.
> [1]
> [2]

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