Your cluster has nodes in seven racks, and you have provided a rack topology script. What is Hadoop's block placement policy, assuming a block replication factor of three?

Question

Options

• AOne copy of the block is written to a node in each of three racks
• BOne copy of the block is written to a node in one rack; two copies are written to two nodes in a different rack
• CAll three of the block are written to nodes on the same rack
• DBecause there are seven racks the block is written to a node on each rack

• A
  5% (1)
• B
  77% (17)
• C
  14% (3)
• D
  5% (1)

Explanation

HDFS uses rack-aware replica placement policy. In default configuration there are total 3 copies of a datablock on HDFS, 2 copies are stored on datanodes on same rack and 3rd copy on a Note: HDFS is designed to reliably store very large files across machines in a large cluster. It stores each file as a sequence of blocks; all blocks in a file except the last block are the same size. The blocks of a file are replicated for fault tolerance. The block size and replication factor are configurable per file. An application can specify the number of replicas of a file. The replication factor can be specified at file creation time and can be changed later. Files in HDFS are write-once and have strictly one writer at any time. HDFS Blocks are replicated?

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