What is Fault Tolerance in HDFS?
Fault-tolerance in HDFS is working strength of a system in unfavorable conditions ( like the crashing of the node, hardware failure and so on). HDFS control faults by the process of replica creation. When client stores a file in HDFS, then the file is divided into blocks and blocks of data are distributed across different machines present in HDFS cluster. And, It creates a replica of each block on other machines present in the cluster. HDFS, by default, creates 3 copies of a block on other machines present in the cluster. If any machine in the cluster goes down or fails due to unfavorable conditions, then also, the user can easily access that data from other machines in the cluster in which replica of the block is present.