For work under umbrella of HADOOP-8468, user can enable nodegroup layer between node and rack in some situations. We should document it after YARN-18 and YARN-19 is figured out.
Add document for enabling node group layer in HDFS
Configurable Hierarchical Topology for YARN
4-layer topology (with NodeGroup layer) implementation of Container Assignment and Task Scheduling (for YARN)
documentation for configuring HVE: dfs.block.replicator.classname should be org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyWithNodeGroup