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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+=============================================
+Retype volumes with different encryptions
+=============================================
+
+https://blueprints.launchpad.net/cinder/+spec/retype-encrypted-volume
+
+Enable the function that changing volume type of a volume [1] to another
+type with different encryptions.
+
+Problem description
+===================
+
+Currently Cinder prevents retyping volumes to a volume type with different
+encryptions.
+
+Use Cases
+=========
+
+* Customers use unencrypted volumes, but later they would like
+  to change the volumes to encrypted.
+* Customers use encrypted volumes and later want to change to unencrypted.
+* Customers want to change encryptions of a volume.
+
+Proposed change
+===============
+
+Allow retype between encrypted and unencrypted volumes.
+Same as current retype mechanism, it allows to retype volumes in available
+and in-use volumes.
+
+If a volume is in available status, the detailed process will be:
+
+* Create a new volume according to new volume_type.
+* Map the two volumes to the volume host.
+* Open the device with dm-crypt if volumes are encrypted. This is done
+  through os-brick/encryptors [2].
+* Copy data from original volume to new volume.
+* Close dm-crypt and detach the volumes.
+* Delete original volume in backend storage.
+
+If a volume is in-use status, nothing needs to change except the bug fix [3].
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+With the feature, it allows users to retype a volume to different
+encryptions.
+
+Security impact
+---------------
+
+Cinder needs to access encryption keys and decrypt the data.
+
+Notifications impact
+--------------------
+
+A flag will be added to current retype notification to show whether
+it needs encryption change.
+
+Other end user impact
+---------------------
+During retyping volumes with different encryptions, Cinder needs to get key.
+But Barbican can be configued only to give key materials to tenants, not admin.
+This may lead that admin can't retype volumes successfully. In such cases,
+Cinder will catch the exception, log the error. The volume to retype will be
+set to original state.
+As os-brick/encryptors doesn't work on RBD, Sheepdog volumes, the function to
+retype such volumes to different encryptions will fail, and volumes will be
+set to original state.
+
+Performance Impact
+------------------
+
+It adds the step of encrypting/decrypting data during retype process,
+and the impact is dependent on the performance of encryption.
+
+Other deployer impact
+---------------------
+
+The feature is dependent on Castellan [4]. Meanwhile, Barbican [5] is currently
+the only key manager backend supported by Castellan. Both the two packages
+are needed.
+
+Developer impact
+----------------
+
+None
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  LisaLi <xiaoyan.li@intel.com>
+
+
+Work Items
+----------
+
+* Remove current limitation which disallows the retype.
+* Attach/detach encrypted volume through dm-crypt.
+
+
+Dependencies
+============
+
+None
+
+
+Testing
+=======
+
+Unit tests need to be created to cover the code change that
+mentioned in "Proposed change".
+New tempest test cases will be added after current retype test [6].
+
+
+Documentation Impact
+====================
+
+The cinder API documentation will need to be updated to describe the change.
+
+References
+==========
+
+* [1]: http://docs.openstack.org/cli-reference/cinder.html#cinder-retype
+* [2]: https://review.openstack.org/#/c/247372/
+* [3]: https://review.openstack.org/#/c/252809/
+* [4]: https://github.com/openstack/castellan
+* [5]: https://github.com/openstack/barbican
+* [6]: https://review.openstack.org/#/c/195443/