Online HDFS Disk Balancer

Kevin Feasel



Lei Xu demonstrates the intra-DataNode disk balancer in HDFS:

By default, the DataNode uses the round-robin-based policy to write new blocks. However, in a long-running cluster, it is still possible for the DataNode to have created significantly imbalanced volumes due to events like massive file deletion in HDFS or the addition of new DataNode disks via the disk hot-swap feature. Even if you use the available-space-based volume-choosing policy instead, volume imbalance can still lead to less efficient disk I/O: For example, every new write will go to the newly-added empty disk while the other disks are idle during the period, creating a bottleneck on the new disk.

Recently, the Apache Hadoop community developed server offline scripts (as discussed inHDFS-1312, the [email protected] mailing list, and GitHub) to alleviate the data imbalance issue. However, due to being outside the HDFS codebase, these scripts require that the DataNode be offline before moving data between disks. As a result, HDFS-1312 also introduces an online disk balancer that is designed to re-balance the volumes on a running DataNode based on various metrics. Similar to the HDFS Balancer, the HDFS disk balancer runs as a thread in the DataNode to move the block files across volumes with the same storage types.

This is a good read and sounds like a very useful feature.

Related Posts

Replicating Data In HDFS Between Clusters

Murali Ramasami and Niru Anisetti have an article showing how to use the Hortonworks Data Lifecycle Manager to set up replication between two Hadoop clusters: Data Lifecycle Manager (DLM) delivers on the promise of location-agnostic, secure replication by encapsulating and copying data seamlessly across physical private storage and public cloud environments. This empowers businesses to […]

Read More

Installing Confluent Platform On Windows

Niels Berglund shows how to install Confluent Platform (the Confluent branded version of Apache Kafka) on a Windows machine using the Windows Subsystem for Linux: WSL is primarily aimed at developers, and it allows you to run Linux environments directly on Windows in a native format and without the overhead of a virtual machine. Let us […]

Read More


October 2016
« Sep Nov »