While installing Openstack using xen as hypervisor, are all the nodes-controller node, compute node configured in DomUs? If yes, then how can compute node access xen which sits directly above hardware as DomU cannot have direct access to hardware.

asked 2014-12-12 08:10:43 -0600

agm123 gravatar image

As DomU cannot directly access the hardware, if compute node is configured in one of the DomU, will it be able to access the Xen. Please clarify me this doubt as soon as possible.

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answered 2014-12-12 09:02:15 -0600

dbaxps gravatar image

View http://www-archive.xenproject.org/fil...
View page 8 :-

Domain 0 to Domain U Communication

As stated earlier, the Xen hypervisor is not written to support network or disk requests
thus a Domain U PV Guest must communicate via the Xen hypervisor with the Domain 0
to accomplish a network or disk request. The example presented below shows a Domain
U PV Guest writing data to the local hard disk.
The Domain U PV Guest PV block driver receives a request to write to the local disk and
writes the data via the Xen hypervisor to the appropriate local memory which is shared
with Domain 0. An event channel exists between Domain 0 and the Domain U PV Guest
that allows them to communicate via asynchronous inter-domain interrupts in the Xen
hypervisor.
Domain 0 will receive an interrupt from the Xen hypervisor causing the PV
Block Backend Driver to access the local system memory reading the appropriate blocks
from the Domain U PV Guest shared memory. The data from shared memory is then
written to the local hard disk at a specific location.
The event channel is shown below as a direct link between Domain 0 and Domain U PV
Guest which is a simplified view of the way the system works. In fact, the event channel
runs through the Xen hypervisor with specific interrupts registered in Xenstored allowing
both the Domain 0 and Domain U PV Guest to quickly share information across local
memory.
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Comments

RH for training usually recommends KVM VMs running on Libvirt subnet to setup Controller,Network,Compute Nodes. They extensively use so called Nested KVM. Ii might be easier for you select Nested KVM on Ubuntu or Fedora or just VMware Workstation for creating mentioned Openstack Nodes.

dbaxps gravatar imagedbaxps ( 2014-12-12 09:12:50 -0600 )edit

Unfortunately , Xen requires in depth understanding of it's architecture to achieve any valuable results. In meantime KVM performance is extremely high due to RH efforts and modern CPUs targeting Hardware Virtualization. Xen merged Mainline Linux ( I mean pvops kernel) several years ago.

dbaxps gravatar imagedbaxps ( 2014-12-12 09:21:27 -0600 )edit

But nothing serious happened on Software Market. KVM virtualization on Fedora 21,Ubuntu 14.X ,CentOS 7 is dominating due to obvious reasons.

dbaxps gravatar imagedbaxps ( 2014-12-12 09:25:46 -0600 )edit

sir, so what i am doing is right? Are all these nodes to be configured in domUs? Could you please give a confirmation so that I can proceed with this??

agm123 gravatar imageagm123 ( 2014-12-13 00:18:09 -0600 )edit

Are all these nodes to be configured in domUs? Yes, you are correct (PV DomUs)

dbaxps gravatar imagedbaxps ( 2014-12-13 00:22:59 -0600 )edit

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Asked: 2014-12-12 08:10:43 -0600

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Last updated: Dec 12 '14