Your cluster has 10 DataNodes, each with a single 1 TB hard drive. You utilize all your disk
capacity for HDFS, reserving none for MapReduce. You implement default replication settings.
What is the storage capacity of your Hadoop cluster (assuming no compression)?

A.
about 3 TB

B.
about 5 TB

C.
about 10 TB

D.
about 11 TB

Explanation:
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 different rack.
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. The NameNode makes all decisions regarding replication
of blocks. HDFS uses rack-aware replica placement policy.
Reference: 24 Interview Questions & Answers for Hadoop MapReduce developers , How the
HDFS Blocks are replicated?