How can i backup and restore the gerrit data (projects, data, changes)?

[mmuejde]

1. The postgres database is empty (only 48MB).
2. I had set all the envs for external database?

[thinkernel]

Most data is moved to NoteDB which is backed by git since 3.0.0.
According to your question about backup and restore, I just backup the volumes. However I use ceph rbd as the docker volume. So I only take a snapshot of the rbd images. There are other methods to backup the docker volumes according to what kind of storage plugin you're using.