There is a bug in openstack Liberty and below where even if you set the config to not zero out volumes upon deletion, it ignores those configuration directives and still zero's out the volume to properly wipe them for security reason's.
Now if you don't care about that because you are doing dev work and need quick deleting volumes you can use the below command to fix the cinder volume driver on the cinder server.
sed -i "s/default='zero'/default='none'/" /usr/lib/python2.7/site-packages/cinder/volume/driver.py
After executing the above command on your cinder server, restart the cinder services
WARNING: Please keep in mine the above is not secure and should not be used in production.
