Comment 1 for bug 1933265

Yes, I have been wondering about this myself.

Apparently there was a major change in snapshot management to the cinder-backup ceph driver:

    https://github.com/openstack/cinder/commit/bc9ab142da919087c71525978f960115ff0259b9
    Bug: https://bugs.launchpad.net/cinder/+bug/1703011

This causes all snapshots created on the source volume of a backup to remain (see https://github.com/openstack/cinder/commit/bc9ab142da919087c71525978f960115ff0259b9#diff-ad4253afa319b756b369399880a46ef8b186e46dbeb6ee06896c243f1f349e6fL716) together with "their" backups. Only if backups are deleted both the snapshots (target as well as source) should be cleaned up.

also see the discussion at https://bugs.launchpad.net/cinder/+bug/1907542

There is a discussion around volumes and their (user hidden) relation to the snapshots they originated from and how to resolve this transparently for the user while maintaining the storage efficiency.

* https://bugs.launchpad.net/cinder/+bug/1677525
* https://review.opendev.org/c/openstack/cinder/+/754397