Grokking the Advanced System Design Interview
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HDFS High Availability (HA)

Let's learn how HDFS achieves high availability.

HDFS high availability architecture

Although NameNode's metadata is copied to multiple file systems to protect against data loss, it still does not provide high availability of the filesystem. If the NameNode fails, no clients will be able to read, write, or list files, because the NameNode is the sole repository of the metadata and the file-to-block mapping. In such an event, the whole Hadoop system would effectively be out of service until a new NameNode is brought online.




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