While operating an HA cluster, the Active NameNode cannot commit a transaction if it cannot write successfully to a quorum of the JournalNodes.
When restarting an HA cluster, the steps for initializing JournalNodes and NN2 can be skipped.
Start the services in the following order:
JournalNodes
NameNodes
Note Verify that the ZKFailoverController (ZKFC) process on each node is running so that one of the NameNodes can be converted to active state.
DataNodes
In a NameNode HA cluster, the following
dfs admin
command option will run only on the active NameNode:-rollEdits
The following
dfs admin
command options will run on both the active and standby NameNodes:-safemode enter -saveNamespace
The
-saveNamespace
option requiressafemode
.