Taiwan Hadoop Forum

最近在準備CCA-410考試,遇到了以下這兩個問題,個人覺得Question 1答案應該是C,Question 2答案應該是D,請各位幫忙看一下我的答案和觀念是否有錯,感謝!

1. Your cluster implements HDFS High Availability (HA). You two NameNodes are named nn01 and nn02. What
occurs when you execute the command:
Hdfs haadmin -failover nn01 nn02
A. nn02 becomes the standby NameNode and nn02 becomes the active NameNode
B. Nn01 is fenced, and nn01 becomes the active NameNode
C. Nn01 is fenced, and nn02 becomes the active NameNode
D. Nn01 becomes the standby NameNode and nn02 becomes the active NameNode


2.Your cluster implements hdfs high availability (HA) your two namenodes are named hadoop01 and hadoop02.
What occurs when you execute the command:
Sudo -u hdfs haadmin failover hadoop01 hadoop02
A. Hadoop02 becomes the standby namenode and hadoop01 becomes the active namenode
B. Hadoop02 is fenced, and hadoop01 becomes active namenode
C. Hadoop01 becomes inactive and hadoop02 becomes the active namenode
D. Hadoop01 is fenced, and hadoop02 becomes the active namenode

請參考 "Hadoop Operations", Chapter 5, P.111

範例 5-12 的命令,手動啟動主要的名稱節點。設定於 -failover 指令的引數是應該進入待命狀態的名稱節點,後面接著應進入主動狀態的名稱節點。答案.....我不明講，請解讀字面意義是否與上面的說明相符

官方文件有寫更細部的邏輯

Source: http://hadoop.apache.org/docs/r2.0.2-alpha/hadoop-yarn/hadoop-yarn-site/HDFSHighAvailability.html

failover - initiate a failover between two NameNodes

This subcommand causes a failover from the first provided NameNode to the second. If the first NameNode is in the Standby state, this command simply transitions the second to the Active state without error. If the first NameNode is in the Active state, an attempt will be made to gracefully transition it to the Standby state. If this fails, the fencing methods (as configured by dfs.ha.fencing.methods) will be attempted in order until one succeeds. Only after this process will the second NameNode be transitioned to the Active state. If no fencing method succeeds, the second NameNode will not be transitioned to the Active state, and an error will be returned.

謝謝Jazz的解惑,小弟今天已經考過了CCA-410

恭喜了 兩張都拿到了~

- Jazz

謝謝 ! 目前正在準備CCB-400 希望能一次過關 !