I have Elasticsearch Data pods that are currently running on an AKS and are connected to Persistent Volumes that is using a Premium SSD Managed Disk Storage Class and I want to downgrade it to Standard SSD Managed Disk without losing the data I have on the currently used Persistent Volume. I've created a new Storage Class that is defined with Standard SSD Managed Disk, but if I create a new PV from that it obviously doesn't keep the old data and I need to copy it somehow, so I was wondering what would be best practice switching PV's Storage Class.
Unfortunately, once a PVC is created and a PV is provisioned for it, the only thing you can change without creating a new one is the volume's size
The only straightforward way I could think of without leveraging CSI snapshots/clones, which you might not have access to (depends on how you created PVCs/PVs AFAIK), would be to create a new PVC and mount both volumes on a Deployment whose Pod has root access and the rsync command.
Running rsync -a /old/volume/mount/path /new/volume/mount/path on such a Pod should get you what you want.
However, you should make sure that you do so BEFORE deleting PVCs or any other resource using your PVs. By default, most of the default storage classes create volumes with reclaim policies that immediately delete the PV as soon as all resources using it are gone, so there's a small risk of data loss