The log was saved to /var/log/anaconda, but our /var is on tempfs which can't save anything after reboot, so save the log to /root/anaconda_log. Another issue is that we don't use the rsyslog, it creates install.log and install.log.syslog in /root, and install.log is null, the install.log.syslog doesn't contain any useful info either, only contains its self start info, so disable it.
