Cloned from launchpad blueprint https://blueprints.launchpad.net/cinder/+spec/generic-volume-migration.
When migrating a volume between two backends, the copy_volume_data routine in the source volume's driver is executed to move the blocks from one volume to another. This routine assumes that both source and destination volumes can be attached locally via iSCSI. This is technically not necessary for local volumes and also prevents drivers such as Ceph from participating in volume migration operations.
I propose that we abstract the iSCSI volume attachement into a routine that can determine the best way to return a file-like python object. For remote volumes, this may fall back to attaching the volume using iSCSI. And for drivers that do not use iSCSI like Ceph, its RBD interface can be hidden behind a similar file-like object such that copy_volume_data does not see this difference.
Blueprint submission via cinder-specs is in progress.
Specification URL (additional information):
*** Bug 1121610 has been marked as a duplicate of this bug. ***
*** Bug 1205621 has been marked as a duplicate of this bug. ***
I believe each driver validates the extra specs and can allow the migration to continue if acceptable. If you can give me a specific example I'd be happy to verify and report back.
'migrate' will move a volume from one host to another if the volume type and backend do not change. 'retype' allows you to change type and backend if desired. Without a migration policy, retype will update metadata (extra specs) but not move the volume data from its current location. If not moving the data means the retype cannot be satisfied, then migration is required where the type also changes. And this is where we connect to both backends, read data from the source, and write it to the destination.
The cinder naming is a little confusing in this regard, let me know if I can clarify any of this.
I think what's there is accurate. For retype, we are missing the case of retyping without migration where the user wants to change the class (or other attribute) of the storage. Is that documented in another section? If not it might be good to include it here.
Also, wether only the admin can issue these commands is dependent on the configuration, it's possible to allow users to migrate and retype their own storage volumes.
This is better, I like it. Thanks Don!
Verification failed due to Bug 1315661
Probably blocked by https://bugzilla.redhat.com/show_bug.cgi?id=1315661
Migration of volume between one pool to another on the same Ceph cluster. In future releases the feature will support migration between Ceph clusters, documented in Bug 1315661
The verification was on
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.