Configuring storage balancing for DataNodes
You can configure HDFS to distribute writes on each DataNode in a manner that balances out available storage among that DataNode's disk volumes.
By default a DataNode writes new block replicas to disk volumes solely on a round-robin basis. You can configure a volume-choosing policy that causes the DataNode to take into account how much space is available on each volume when deciding where to place a new replica.
- how much DataNode volumes are allowed to differ in terms of bytes of free disk space before they are considered imbalanced, and
- what percentage of new block allocations will be sent to volumes with more available disk space than others.