Your cluster implements HDFS High Availability (HA). Your 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 nn01 becomes the active NameNode
B.
nn02 is fenced, and nn01 becomes the active NameNode
C.
nn01 becomes the standby NamNode and nn02 becomes the active NAmeNode
D.
nn01 is fenced, and nn02 becomes the active NameNode
C
failover causes nn02 to become active namenode.
if nn01 is already in standby state nothing is done to it and nn02 transitions to active state.
if nn01 is in the active state first it will be gracefully transitioned to standby if that fails it will be fenced and transitions to standby and nn02 becomes active.
if nn01 fencing also fails the command fails and nn02 does not become active.
http://www.cloudera.com/documentation/archive/cdh/4-x/4-2-1/CDH4-High-Availability-Guide/cdh4hag_topic_2_7.html
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