HDFS High Availability (HA)

Backing up the FsImage and EditLog stops the NameNode from losing metadata. It does nothing for the half hour an administrator needs to bring a new NameNode up. This lesson looks at how HDFS closes that gap, and stays available straight through a NameNode failure.

HDFS high availability architecture

Copying the NameNode's metadata to multiple file systems protects the data, but not the service. If the NameNode fails, every client stops. No reads, no writes, no listing files, because the NameNode is the only place holding the metadata and the map from files to blocks