If the messages log is be flushed by the history information, view the messages_bak log. If the messages_bak log is flushed too, try to view the messages in his_tar_powerlost_time.tgz under \OSM\log_conf_local\log\his_debug.
View the messages after the OSM is restarted. The first a few lines of the log file contains syslogd:
Mar 29 11:51:00 OceanStor syslogd 1.4.1: restart.