Ceph » rgw

The COPY operation can copy data between buckets without involving the client.

In Amazon's words,

In addition to the obvious use for this feature -- creating a new S3 object from an existing one -- you can also use it to rename an object within a bucket or to move an object to a new bucket. You can also update the metadata for an object by copying it to itself while supplying new metadata.

osync should use the COPY operation to copy data between buckets that are on the same host, instead of doing a GET followed by a PUT.
This would be a nice optimization.