One of the following descriptions about the HDFS federation of the Hadoop distributed file system is correct? (Multiple choices)

HDFS Federation is an architecture designed to overcome the scalability limitations of a single NameNode in a large Hadoop cluster. It achieves this by using multiple, independent NameNodes. Each NameNode manages a distinct portion of the file system, known as a namespace. Each namespace is associated with its own block pool, which is a logical grouping of all data blocks belonging to that namespace. While the block pools are logically separate, all NameNodes in the federation utilize a common set of DataNodes for physical block storage. This design allows for the horizontal scaling of the namespace layer, as more NameNodes can be added to the cluster to support more files and metadata.

B. One namespace can use multiple block pools to manage data blocks. This is incorrect. The HDFS Federation architecture maintains a strict one-to-one mapping between a namespace and a block pool to ensure logical isolation and simplify management.

1. Apache Hadoop Documentation. HDFS Federation. In the official documentation for Hadoop 3.3.6, the architecture section explicitly details the relationship between NameNodes, namespaces, and block pools.

Reference for A, C, D: "In order to scale the name service horizontally, HDFS Federation uses multiple independent NameNodes/namespaces... Each NameNode manages a namespace volume, which is made up of the metadata for the namespace, and a block pool which contains all the blocks for the files in the namespace... DataNodes store blocks for all the block pools in the cluster." This confirms that a namespace uses a block pool (A), the physical storage is shared while logical pools are isolated (C), and the primary purpose is horizontal expansion (D).

Reference for B (Incorrect): The same documentation describes a singular relationship: "a block pool which contains all the blocks for the files in the namespace," implying a one-to-one relationship, not one-to-many.

2. Gautam, J., & Singh, S. (2015). A Survey on HDFS Federation for Big Data Storage. International Journal of Computer Applications, 113(17), 1-4.

Reference for A, C, D: (Section 3, HDFS Federation Architecture) "Each NameNode manages its own namespace and block pool... All the NameNodes share the same set of DataNodes. The DataNodes store the data blocks from multiple block pools... HDFS Federation scales the namespace horizontally." This peer-reviewed article corroborates the core principles of federation: the namespace-to-block-pool link, shared physical storage with logical isolation, and horizontal scalability.