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How to launch a VM that use dev=vda and bus=virtio using nova??

asked 2018-02-14 08:22:31 -0500

vathanlal gravatar image

updated 2018-02-14 09:39:36 -0500

Hello,

My OpenStack cluster(newton) is based on KVM virtualization. I found that all the instances Iam launching is using dev=sda and bus=scsi. How can I launch an Instance that using dev=vda and bus=virtio?? Or I want to make virtio as default for all VMs.

I tried to set the image-property as below

glance image-update --property hw_disk_bus=virtio 30393b62-c98e-4282-9fcc-0acc307f0c01

Then I tried to launch a new instance with this image but still it is using dev=sda and bus=scsi. I dont know how to change it. Is there any option exists for this?? Any help is really appreciated.

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If you enable debug logging, you will see in the nova-compute log how the libvirt xml file is built. I don’t know what debug messages are issued, but perhaps the reason for selecting the SCSI bus becomes clear as well.

Bernd Bausch gravatar imageBernd Bausch ( 2018-02-14 16:18:18 -0500 )edit

I enabled debug option and I found driver.py is responsible for creating the .xml file. But it doesn't give much information. I dont have any idea or any sufficient documents how to change nova libvirt to use virtio by default.

vathanlal gravatar imagevathanlal ( 2018-02-15 10:01:10 -0500 )edit
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answered 2018-02-14 09:09:55 -0500

eblock gravatar image

Hi, you can control that with the image's metadata:

control:~ # openstack image set --property hw_scsi_model=virtio-scsi --property hw_disk_bus=scsi --property hw_qemu_guest_agent=yes --property os_require_quiesce=yes 8a143d74-565f-47d8-b10d-0dd5842976aa

This will enable devices like /dev/sdX. Maybe this is the default in your environment, if I just remove these properties from the base image my instances get their /dev/vdX devices. You should take look into your configs, maybe you have defined some default image properties. You can disable these properties per image bye simply running:

control:~ # openstack image set --remove-property hw_scsi_model --remove-property hw_disk_bus --remove-property hw_qemu_guest_agent --remove-property os_require_quiesce 8a143d74-565f-47d8-b10d-0dd5842976aa

Hope this helps!

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Thanks for the response. I tried this by first removing all the properties of the image and then adding a new property hw_disk_bus=virtio and launch a VM from this image. But still the same result. It is using scsi and sda not virtio. I updated the question please go through it. Thanks.

vathanlal gravatar imagevathanlal ( 2018-02-14 09:42:10 -0500 )edit

Besides debugging logs, could you check if your base image has the required modules? On your VM run

find /lib/modules/ -name *virt*
eblock gravatar imageeblock ( 2018-02-15 07:41:25 -0500 )edit

Something like this would be needed:

host:~ $ find /lib/modules/ -name *virt*
/lib/modules/4.4.104-39-default/kernel/drivers/virtio
/lib/modules/4.4.104-39-default/kernel/drivers/virtio/virtio_ring.ko
/lib/modules/4.4.104-39-default/kernel/drivers/virtio/virtio_balloon.ko
eblock gravatar imageeblock ( 2018-02-15 07:42:59 -0500 )edit

Maybe this article helps a little.

eblock gravatar imageeblock ( 2018-02-15 07:44:40 -0500 )edit

Thanks for the response. Actually I updated my compute node OS(ubuntu16.04) it was a regular security update. After that nova is using only scsi and all the VM's have ALERT! LABEL=cloudimg-rootfs does not exist. Dropping to a shell! error. Before that I can create instances fine. They use virtio.

vathanlal gravatar imagevathanlal ( 2018-02-15 10:45:32 -0500 )edit
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Asked: 2018-02-14 08:22:31 -0500

Seen: 1,647 times

Last updated: Feb 14 '18

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