高可用性检查点
Checkpointing in high availability
在Hadoop高可用中，Check pointing是由哪个节点完成的？
除了做检查指向的主备节点之外，是否还有二级名称节点？
备用 NameNode 保持足够的状态以进行快速故障转移
[I]n an HA cluster, the Standby NameNode also performs checkpoints of the namespace state, and thus it is not necessary to run a Secondary NameNode, CheckpointNode, or BackupNode in an HA cluster. In fact, to do so would be an error
Is there a secondary name node in addition to the active and the stand-by nodes
只有一主一备，如该页所述。
Currently, only a maximum of two NameNodes may be configured per nameservice
在Hadoop高可用中，Check pointing是由哪个节点完成的？ 除了做检查指向的主备节点之外，是否还有二级名称节点？
备用 NameNode 保持足够的状态以进行快速故障转移
[I]n an HA cluster, the Standby NameNode also performs checkpoints of the namespace state, and thus it is not necessary to run a Secondary NameNode, CheckpointNode, or BackupNode in an HA cluster. In fact, to do so would be an error
Is there a secondary name node in addition to the active and the stand-by nodes
只有一主一备，如该页所述。
Currently, only a maximum of two NameNodes may be configured per nameservice