Cinder create snapshot failed with Ceph as backend, Why ?

Issue

• Cinder create snapshot failed with Ceph as backend, Why ?
• Openstack cinder logs :

2015-10-19 12:44:27.653 21119 INFO cinder.volume.manager [req-d3467fa6-8bc0-427e-9a9f-08afd90a47db 5ae0a62445ed40b7a1bcc61befbb7a4f 5271549144f34421b60ab549a13e3c8a - - -] snapshot 8e536e20-a431-4c24-8706-4e5291ab7141: creating
2015-10-19 12:44:27.679 21119 DEBUG cinder.volume.manager [req-d3467fa6-8bc0-427e-9a9f-08afd90a47db 5ae0a62445ed40b7a1bcc61befbb7a4f 5271549144f34421b60ab549a13e3c8a - - -] snapshot 8e536e20-a431-4c24-8706-4e5291ab7141: creating create_sn
apshot /usr/lib/python2.7/site-packages/cinder/volume/manager.py:648
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2015-10-19 12:44:27.762 21119 TRACE oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/cinder/volume/drivers/rbd.py", line 701, in create_snapshot
2015-10-19 12:44:27.762 21119 TRACE oslo_messaging.rpc.dispatcher     volume.create_snap(snap)
2015-10-19 12:44:27.762 21119 TRACE oslo_messaging.rpc.dispatcher   File "/usr/lib/python2.7/site-packages/rbd.py", line 590, in create_snap
2015-10-19 12:44:27.762 21119 TRACE oslo_messaging.rpc.dispatcher     raise make_ex(ret, 'error creating snapshot %s from %s' % (name, self.name))
2015-10-19 12:44:27.762 21119 TRACE oslo_messaging.rpc.dispatcher InvalidArgument: error creating snapshot snapshot-8e536e20-a431-4c24-8706-4e5291ab7141 from volume-e4d54c33-555c-4e62-ad96-e8265f4a7639

• Ceph RBD client side logs :

2015-10-27 09:23:29.913396 7fcc8ea0c740 -1 librbd: failed to create snap id: (22) Invalid argument
2015-10-27 09:23:29.913472 7fcc8ea0c740 20 librbd: close_image 0x4837050