HOWTO: Change replication factor of existing files in HDFS

There are references around the web regarding changing the replication factor on a running Hadoop system. For example, if you don’t have even distribution of blocks across your Datanodes, you can increase replication temporarily and then bring it back down.

To set replication of an individual file to 4:

./bin/hadoop dfs -setrep -w 4 /path/to/file

You can also do this recursively. To change replication of entire HDFS to 1:

./bin/hadoop dfs -setrep -R -w 1 /

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