[ceph-users] RBD clone on Bluestore

hello! I'm trying to understand how Bluestore cooperates with RBD image clones, so my test is simple 1. create an image (2G) and fill with data 2. create a snapshot 3. protect it 4. create a clone of the image 5. write a small portion of data (4K) to clone 6. check how it changed and if just 4K are used to prove CoW allocated new extent instead of copying out snapped data. Unfortunately it occurs that at least rbd du reports that 4M was changed and the clone consumes 4M of data instead of expected 4K... ''' rbd du rbd/clone1 NAME PROVISIONED USED clone1 2 GiB 4 MiB ''' How can I trace/prove Bluestore CoW really works in this case, and prevent copying the rest of the 4M stripe like Filestore did ? p.s tested on Luminous/Octopus, ssd devices, min_alloc_size: 16k, block_size: 4k best regards! -- Pawel S.