Shrink Kubernetes persistent volumes

I do have multiple persistent volumes which need to be shrinked to reduce the hosting costs. I already figured out that Kubernetes does not provide such an option. I also tried to clone or the restore the volumes from an snapshot to a new smaller volume - with the same result (requested volume size XXX is less than the size XXX for the source snapshot).

Nevertheless I need a solution or workaround to get this done.

The cluster is deployed with Rancher and the volumes are mounted to a Ceph Cluster. Everything is provided by an external hoster.

Solution

Finally I achieved what needed with the following steps (still tricky and manual work):

Stop running pod (otherwhise you could not use the volume in the next steps)
Create the a new PVC with the desired capacity (ensure that the spec and label matches the exisitng PVC)
Run this Job https://github.com/edseymour/pvc-transfer
- In the spec of the job-template.yaml set the source and destination volume
Set the ReclaimPolicy on the new created pv to Retain. This will ensure that the pv won't be deleted after we delete the temp pvc in the next step
Delete the source and destination pvc
Create a new pvc with the old name and the new storage capacity
On the new pv point the claimRef to the new pvc