Cluster Rebalancing

Kevin Feasel

2016-07-22

Hadoop

Peter Coates discusses cluster rebalancing in Hadoop:

After adding new racks to our 70 node cluster, we noticed that it was taking several hours per terabyte to rebalance the nodes. You can copy a terabyte of data across a 10GbE network in under half an hour with SCP, so why should HDFS take several hours?

It didn’t take long to discover the cause—the configuration parameterdfs.datanode.balance.bandwidthPerSecond controls how much bandwidth each node is allowed to use for rebalancing, and it defaults to a conservative value of 10Mb/sec/node, which is 1.25MB/sec. If you have 70 nodes (the number we started with before adding new ones), that’s 87.5MB/second. One terabyte, i.e., a million MB, divided 87.5MB/sec, equals 11,428 sec, or 3.17 hours per TB. The more nodes in the original cluster, the faster it will write.

On the development side, “it’ll automatically rebalance without us having to worry” is a great thing.  On the administrative side, we’re paid to worry about these things…

Related Posts

Kafka Connect Converters And Serialization

Robin Moffatt goes into great detail on Apache Kafka Connect converters and serialization techniques: Kafka Connect is modular in nature, providing a very powerful way of handling integration requirements. Some key components include: Connectors – the JAR files that define how to integrate with the data store itself Converters – handling serialization and deserialization of […]

Read More

Tuning Apache Spark Applications

Vidisha Gupta has a few tips for tuning Apache Spark programs: Data Serialization – Serialization plays an important role in increasing the performance of any application. Spark provides two serialization libraries – Java Serialization: By default, spark uses Java’s ObjectOutputStream framework which can work with any class that implements java.io.serializable. This serialization is flexible but slow and […]

Read More

Categories

July 2016
MTWTFSS
« Jun Aug »
 123
45678910
11121314151617
18192021222324
25262728293031