HDFS Replica Placement Policy

As per the replica placement policy in Hadoop each HDFS block is replicated across different nodes. Default replication factor is 3 which means by default each HDFS block is replicated on three different nodes in order to make HDFS reliable and fault tolerant. Considerations for HDFS replica placement policy When…

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Namenode in Safemode

This post shows what is Safemode in Namenode and what are the configurations for the safemode in Hadoop. You will also see the commands available to enter and leave the safemode explicitly. When the Namenode is started it loads the file system state into memory initially from the fsimage and…

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HDFS High Availability

In this post we’ll see what is HDFS high availability, high availability architecture and the configuration needed for HDFS high availability in Hadoop cluster. Some background on HDFS high availability Prior to Hadoop 2, the NameNode was a single point of failure (SPOF) in an HDFS cluster. In a HDFS cluster there’s…

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