Comment 2 for bug 2018001

I think we've figured this out. In Victoria, storage assisted migration was added to Solidfire:
https://review.opendev.org/c/openstack/cinder/+/746941. So prior to Victoria, cinder retype
was a host assisted migration using the generic cinder driver.

After Victoria, it's now handled by the Solidfire driver as a storage assisted migration. And
it looks like cinder retype (when run as a storage assisted migration) on works for volume migrations
between two solidfire clusters: https://github.com/openstack/cinder/commit/b1d6210d454c05aeca2fbe944c6b6e82c508372f#diff-a62544f589ca8b9ea1f17078ec5fb30aa687f3dde2b8125b1928cf244832f6b9R2425.

To workaround this, you can't use a volume type that has the "volume_backend_name" property set.
Essentially you can't refer to the backend at all it seems. If you instead create a volume type
with the "vendor_name='NetApp'" property, it looks like it reverts to a host assisted migration and the cinder retype works.