/tmp/.cloudera_health_monitoring_canary_files
1. Server01 또는 02에 Putty로 접속
2. Safe Mode Is On 상태 확인
$ hdfs dfsadmin -safemode get
3. Safe Mode 해제 명령 수행
$ hdfs dfsadmin -safemode leave
HDFS Service Advanced Configuration Snippet (Safety Valve) for hdfs-site.xml
dfs.client.socket-timeout
3000000
dfs.datanode.socket.write.timeout
3000000