Open Stack

We are currently installing a new openstack cluster (Liberty) with 
openstack-ansible and an already existing ceph cluster. We have both 
images and volumes located in ceph with rbd. My current problem is that 
snapshots take a very long time and I can see that snapshots are 
temporary created under /var/lib/nova/instances/snapshots/tmp on the 
compute node, I thought that this would not be needed when using ceph? 
The instance that I am creating a snapshot of uses a raw image that is 
protected. What can cause this behavior?

Thanks,
Andreas