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[Thierry Carrez <thierry.carrez+lp@xxxxxxxxx>]

** Changed in: nova
       Status: Fix Committed => Fix Released

** Changed in: nova
    Milestone: None => juno-3

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https://bugs.launchpad.net/bugs/1282643

Title:
  block/live migration doesn't work with LVM as libvirt storage

Status in OpenStack Compute (Nova):
  Fix Released

Bug description:
  ## What we did:

  We were trying to use block migration in a setup that use LVM as
  libvirt storage:

  nova live-migrate --block-migrate <uuid> <host-name>

  ## Current Result:

  Nothing happens, no migration, but in libvirtd.log of the destination
  hypervisor we saw:

     error : virNetClientProgramDispatchError:175 : Failed to open file
  '/dev/instances/instance-0000015f_disk': No such file or directory

  the /dev/instances/instance-0000015f_disk is the root disk of our
  instance.

  ## What we found:

  After a bit of wondering in the code of nova, we saw that nova in the
  destination host actually fails to create the instance resources. This
  should have been done as part of pre_live_migration RPC call, but this
  one doesn't receive any disks in the disk_info argument
  (https://github.com/openstack/nova/blob/stable/havana/nova/virt/libvirt/driver.py#L4132)
  except the config disk. We found that this due to the fact that LVM
  disks (e.g. root disk) are skipped by driver.get_instance_disk_info
  method, specially by this line
  https://github.com/openstack/nova/blob/master/nova/virt/libvirt/driver.py#L4585-L4587,
  which skip any disk that is not a file thinking that it must be a
  block storage which not true because LVM disk are created as a block
  type
  (https://github.com/openstack/nova/blob/stable/havana/nova/virt/libvirt/imagebackend.py#L358),
  snippets for the libvirt.xml below:

   <devices>
      <disk type="block" device="disk">
        <driver name="qemu" type="raw" cache="none"/>
        <source dev="/dev/instances/instance-00000163_disk"/>
        <target bus="virtio" dev="vda"/>
      </disk>
      <disk type="file" device="cdrom">
        <driver name="qemu" type="raw" cache="none"/>
        <source file="/var/lib/nova/instances/6ed79840-c850-498f-9607-ffa92e7cf944/disk.config"/>
        <target bus="ide" dev="hdd"/>
      </disk>
      <interface type="bridge">
        <mac address="fa:16:3e:f0:61:24"/>
        <model type="virtio"/>
        <source bridge="brqe914da2f-c4"/>
        <target dev="tap258425f6-9b"/>
      </interface>
      <serial type="file">
        <source path="/var/lib/nova/instances/6ed79840-c850-498f-9607-ffa92e7cf944/console.log"/>
      </serial>
      <serial type="pty"/>
      <input type="tablet" bus="usb"/>
      <graphics type="vnc" autoport="yes" keymap="en-us" listen="0.0.0.0"/>
    </devices>

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