Does elasticsearch need a persistent storage when deployed on kubernetes?
The warning is so that folks don't assume that using emptyDir provides a persistent storage layer. An emptyDir volume will persist as long as the pod is running on the same host. But if the host is replaced or it's disk becomes corrupted, then all data would be lost. Using network mounted storage is one way to work around both of these failure modes. If you want to use replicated storage instead, that works as well.