Document volume migration

[candlerb]

For operational reasons, you might want to move a zfs dataset to another node.

The actual dataset movement is straightforward, thanks to tools like zrepl, sanoid etc. I'm also not worried about having to shut down any pod using it first.

But I'm not sure how best to update k8s with the new info. Is it possible to update the existing pv and pvc to reference the new node? Is it possible to create a new pvc which "adopts" an existing zfs dataset?

I guess at worst, the process might be:

• create a new pvc
  • need to be able to force it onto the right node
  • this in turn may require a temporary pod with node affinity
  • delete the temporary pod but keep the pvc
• find the zfs dataset it has just created
• delete it, and in its place sync across the source zfs dataset
• start the "real" application pod with the new pvc