OK, backing and restoring ldap database I get an error:
[zimbra@orion ~]$ openldap/sbin/slapadd -f /opt/zimbra/conf/slapd.conf -l /tmp/ldap.ldif
The first database does not allow slapadd; using the first available one (2)
bdb_db_open: Warning - No DB_CONFIG file found in directory /opt/zimbra/openldap-data: (2)
Expect poor performance for suffix .
So, I restored DB_CONFIG from a backup and I got more nasty errors.
I attempted to restore the db but that didn't work either.