I wanted to flag that I think this is not a good design.

failed to set the setting priority-class with invalid value rancher-critical: cannot modify priority class setting before all volumes are detached

The change should be put in place and applied when possible, without causing downtime. There is no easy way to detach all volumes without scaling all workload to 0, which is painful. Maybe a kill/maintenance switch in longhorn can be implemented to facilitate such changes in an easier manner.

Hello Before applying the change of the priority class, we have to stop the longhorn pods first. The idea from Shuo looks feasible and can be an improvement. Can you help create a ticket for the feature request on GitHub issue? Thank you.