Final answer:
The true statement about HDFS is that C. it replicates data for fault tolerance. HDFS ensures data availability even if some nodes fail, by distributing multiple copies of data across the cluster.
Step-by-step explanation:
The question relates to the Hadoop Distributed File System (HDFS), which is a fundamental component of the Hadoop software framework. When considering the true statement about HDFS, option C is correct: It replicates data for fault tolerance. HDFS creates multiple copies of data blocks and distributes them across different nodes within the cluster to ensure that the system is tolerant to faults. If one node fails, the data can still be accessed from another node. This replication strategy is a core aspect of HDFS and ensures data availability and durability.
Option A is incorrect because HDFS does not require data to be stored in a structured format; it is designed to handle large volumes of data in any format, structured or otherwise. Option B relates more to the processing frameworks like MapReduce or Apache Spark that run on top of HDFS and are responsible for high-speed data processing. Lastly, option D is incorrect because HDFS does not require a relational database to operate. It can function independently as a storage layer within the Hadoop ecosystem.