Apache Hadoop is an open source to load and process the big data efficiently.
Cloudera, Hortonworks, MapR etc.
There are two major component of Hadoop. One is HDFS to store your data and Map Reduce to process your data.
copyFromLocal, put and moveFromLocal.For Detail Click Here
copyToLocal and get command.
Hadoop fs –ls.
Hadoop fs –mkdir dir_nameFor Detail Click Here
Default replication is 3 in distributed mode.
Combiner is also known as mini reducer for map reduce program. It is used to enhance the performance. Combiner processes the large output of mapper and filters and summarizes it and then passes it to reducer for efficient and fast process.