Hadoop Format Steps

1. stop hadoop service (/usr/local/hadoop/bin/stop-all.sh)
2. login root user
3. rm -rf /mnt/sdb1/* in all servers
4. login as hduser
5. /usr/local/hadoop/bin/hadoop namenode -format in all servers
6. start hadoop service as hduser(/usr/local/hadoop/bin/start-all.sh)