Cinder volume migration

cinder.volume.manager._migrate_volume_generic (https://github.com/openstack/cinder/blob/master/cinder/volume/manager.py#L1623)
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cinder.volume.manager._copy_volume_data(src, dest) (https://github.com/openstack/cinder/blob/master/cinder/volume/manager.py#L1681)
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will try to attach 'src' and 'dest' volumes to the c-vol manager's host to copy volume data using `dd` tool
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cinder.volume.manager._attach_volume (https://github.com/openstack/cinder/blob/master/cinder/volume/manager.py#L1532)
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calls initialize_connection
calls _connect_device
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cinder.volume.manager._connect_device (https://github.com/openstack/cinder/blob/master/cinder/volume/manager.py#L1504)
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gets connector from os-brick an calls connect_volume
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connect_volume
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vol_utils.copy_volume(src_dev, dest_dev)
BUT: connect_volume doesn't `attach` volume for every protocol!