On Kubernetes 1.15 thru 1.18, cloning Apache Cassandra clusters across namespaces using pure Kubernetes/kubectl.
Includes code on GitHub at, tinyurl.com/ddn3000
the May/2021 article.
Video on YouTube at, https://www.youtube.com/watch?v=paly5VVuAYM
These same techniques can copy PVs/PVCs across namespaces.