Ceph » rbd

This appears to be fairly easy to hit when combined with auto-deletion of trashed snapshots:

$ rbd snap create a@snap
Creating snap: 100% complete...done.
$ rbd clone --rbd-default-clone-format 2 a@snap b
$ rbd snap rm a@snap
Removing snap: 100% complete...done.
$ rbd flatten b

$ rbd info b
rbd image 'b':
        size 1 GiB in 256 objects
        order 22 (4 MiB objects)
        snapshot_count: 0
        id: 47904bf44ef0
        block_name_prefix: rbd_data.47904bf44ef0
        format: 2
        features: layering, deep-flatten, operations
        op_features: clone-child
        flags: 
        create_timestamp: Thu Sep 30 07:28:38 2021
        access_timestamp: Thu Sep 30 07:28:38 2021
        modify_timestamp: Thu Sep 30 07:28:38 2021
        parent: rbd/a@5272fce1-e70c-44f9-a7b5-ba52828ab6e7
        overlap: 1 GiB
$ rbd info b
2021-09-30T07:28:45.707-0400 7f9709aa4700 -1 librbd::image::OpenRequest: failed to set image snapshot: (2) No such file or directory
2021-09-30T07:28:45.711-0400 7f970a2a5700 -1 librbd::image::RefreshParentRequest: failed to open parent image: (2) No such file or directory
2021-09-30T07:28:45.711-0400 7f970a2a5700 -1 librbd::image::RefreshRequest: failed to refresh parent image: (2) No such file or directory
2021-09-30T07:28:45.711-0400 7f970a2a5700 -1 librbd::image::OpenRequest: failed to refresh image: (2) No such file or directory
rbd: error opening image b: (2) No such file or directory
$ rbd info b
rbd image 'b':
        size 1 GiB in 256 objects
        order 22 (4 MiB objects)
        snapshot_count: 0
        id: 47904bf44ef0
        block_name_prefix: rbd_data.47904bf44ef0
        format: 2
        features: layering, deep-flatten
        op_features: 
        flags: 
        create_timestamp: Thu Sep 30 07:28:38 2021
        access_timestamp: Thu Sep 30 07:28:38 2021
        modify_timestamp: Thu Sep 30 07:28:38 2021

ceph-csi calls "rbd info" in a number of places and sporadic ErrImageNotFound failures result in stale images being left behind (i.e. a slowly-growing space leak).