HDFS high availability in Hadoop - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is HDFS High Availability (HA)?

HDFS High Availability means having two NameNodes: one active and one standby. This setup helps keep the system running even if one NameNode fails.

beginner

Why do we need a standby NameNode in HDFS HA?

The standby NameNode takes over if the active NameNode fails. This prevents downtime and data loss.

intermediate

What is the role of ZooKeeper in HDFS HA?

ZooKeeper helps manage which NameNode is active by coordinating failover automatically.

intermediate

What is a Quorum Journal Manager (QJM) in HDFS HA?

QJM is a shared storage system that keeps edit logs from the active NameNode. Both NameNodes use it to stay in sync.

intermediate

How does automatic failover work in HDFS HA?

If the active NameNode fails, ZooKeeper detects it and switches the standby NameNode to active, so the system keeps working without manual help.

What does HDFS High Availability primarily prevent?

A System downtime due to NameNode failure

B Data replication across DataNodes

C Slow data processing

D Network congestion

HDFS HA prevents downtime by having a standby NameNode ready to take over if the active one fails.

Which component helps coordinate failover in HDFS HA?

A ZooKeeper

B DataNode

C ResourceManager

D NameNode

ZooKeeper manages which NameNode is active and handles automatic failover.

What is stored in the Quorum Journal Manager?

A User data files

B Configuration files

C Backup snapshots

D Edit logs from the active NameNode

QJM stores edit logs to keep both NameNodes synchronized.

How many NameNodes are active at the same time in HDFS HA?

A Two

B One

C None

D Depends on cluster size

Only one NameNode is active; the other is standby.

What happens if the active NameNode fails in an HA setup?

A Data is lost

B The cluster stops working

C The standby NameNode becomes active automatically

D Manual restart is required

The standby NameNode automatically takes over to keep the system running.

Explain how HDFS High Availability works to keep the system running without downtime.

Think about how two NameNodes share work and how the system switches between them.

Describe the role of ZooKeeper and Quorum Journal Manager in HDFS High Availability.

Focus on coordination and data sharing between NameNodes.