Online HDFS Disk Balancer

Kevin Feasel

2016-10-19

Hadoop

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

Databricks Runtime 5.2 Released

Nakul Jamadagni announces Databricks Runtime 5.2: Delta Time TravelTime Travel, released as an Experimental feature, adds the ability to query a snapshot of a table using a timestamp string or a version, using SQL syntax as well as DataFrameReader options for timestamp expressions.Sample codeSELECT count() FROM events TIMESTAMP AS OF timestamp_expressionSELECT count() FROM events VERSION AS OF version Time travel looks a bit like temporal tables in SQL Server.

Read More

Kafka And The Differing Aims Of Data Professionals

Kai Waehner argues that there is an impedence mismatch between data engineers, data scientists, and ML production engineers: Data scientists love Python, period. Therefore, the majority of machine learning/deep learning frameworks focus on Python APIs. Both the stablest and most cutting edge APIs, as well as the majority of examples and tutorials use Python APIs. […]

Read More

Categories

October 2016
MTWTFSS
« Sep Nov »
 12
3456789
10111213141516
17181920212223
24252627282930
31