Although live migration does work for some vhosts from one kvm host to another, it causes error messages for some other vhosts using the same kvm hosts. The log files deliver hints to an unstoppable block job:

root@qkvm55:~# virsh migrate --live --undefinesource --persistent \
--domain testhost --desturi qemu+ssh://kvm56/system
error: operation failed: migration job: unexpectedly failed
 
root@kvm55:~# tail -n 3 /var/log/libvirt/libvirtd.log
2016-09-02 09:33:35.496+0000: 5978: error : qemuMigrationUpdateJobStatus:2314 :
operation failed: migration job: unexpectedly failed
2016-09-02 09:33:35.498+0000: 5978: warning : qemuMigrationCancelDriveMirror:1916 :
Unable to stop block job on drive-ide0-0-0

The error cause is unknown.

Some sources suggest a downgrade to libvirt-bin version v1.1.0. This solution can not be applied due to the following reasons:

• All KVM hosts of a site better use a common kvm version.
• Taking next Ubuntu migrations into account it is neither helpful nor possible to do a downgrade.
• The solution suggested a downgrade from v1.1.1 to v1.1.0.
• On the affected hosts version v1.2.12 is in use for which no other errors are known.

A live migration is not possible for the affected hosts. They have to be migrated by other means. One opportunity is offline migration:

• Define the vhost on the destination kvm host
• Shut down the vhost on the source kvm host
• Start the vhost on the destination kvm host
• Remove the vhost from the source kvm host

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