[cinder] nfs in kolla

Hello, I' just deployed ocata with kolla and my cinder backend is nfs. Volumes are created successfully but live migration does not work. While cinder_volume container mounts the cinder nfs backend, the cinder api not and during live migration the cinder api logs reports errors accessing volumes :

Stderr: u"qemu-img: Could not open '/var/lib/cinder/mnt/451bacc11bd88b51ce7bdf31aa97cf39/volume-4889a547-0a0d-440e-8b50-413285b5979c'

Any help, please ? Regards Ignazio