For some reason, I make a backup of zimbra by copying 4 directories: /opt/zimbra/store, db, index, openldap-data. Then I remove the old zimbra (M2), install the GA version.
Then I copy these folders to /zimbra with the same permission as they have.

Stop zimbra, start it, in "Starting mta..." step, it require "Password:...".
So, why its require password, and which pwd it needs?
This way of backup old data is okay ?