What is a rack in Hadoop?

A Rack is a collection nodes usually in 10 of nodes which are closely stored together and all nodes are connected to a same Switch. When an user requests for a read/write in a large cluster of Hadoop in order to improve traffic the namenode chooses a datanode that is closer this is called Rack Awareness .

What is rack and rack awareness in Hadoop?

Introduction to HDFS Rack Awareness Rack Awareness in Hadoop is the concept that chooses closer Datanodes based on the rack information. By default, Hadoop installation assumes that all the nodes belong to the same rack. To improve network traffic while reading/writing HDFS files in large clusters of Hadoop.

What is rack in cluster?

The rack is a physical collection of nodes in our Hadoop cluster (maybe 30 to 40). A large Hadoop cluster is consists of many Racks.

What is rack awareness why it is used in Hadoop?

Rack Awareness enables Hadoop to maximize network bandwidth by favoring the transfer of blocks within racks over transfer between racks. Especially with rack awareness, the YARN is able to optimize MapReduce job performance. It assigns tasks to nodes that are ‘closer’ to their data in terms of network topology.

How many racks are in a cluster?

A cluster can occupy one rack or multiple racks. The total number of racks for each cluster type depends on your scalability needs. In each availability zone, place the management cluster and the shared edge and compute cluster in the same rack.

What is cluster in Hadoop?

A Hadoop cluster is a collection of computers, known as nodes, that are networked together to perform these kinds of parallel computations on big data sets.

What does rack aware mean?

Rack awareness is having the knowledge of Cluster topology or more specifically how the different data nodes are distributed across the racks of a Hadoop cluster.

What is rack awareness and why is it necessary?

Rack awareness ensures that the Read/Write requests to replicas are placed to the closest rack or the same rack. This maximizes the reading speed and minimizes the writing cost. Rack Awareness maximizes the network bandwidth by block transfers within the rack.

What is rack in Kafka?

Kafka’s rack awareness feature spreads replicas of the same partition across different failure groups (rack and availability zones). This extends the guarantees Kafka provides for broker-failure to cover rack and/or AZ failures, limiting the risk of data loss should all the brokers in a rack/AZ fail at once.

What is rack topology in Hadoop?

Hadoop keeps multiple copies for all data that is present in HDFS. If Hadoop is aware of the rack topology, each copy of data can be kept in a different rack. By doing this, in case an entire rack suffers a failure for some reason, the data can be retrieved from a different rack.

What is rack awareness in a Hadoop cluster?

HDFS stores files across multiple nodes (DataNodes) in a cluster. To get the maximum performance from Hadoop and to improve the network traffic during file read/write, NameNode chooses the DataNodes on the same rack or nearby racks for data read/write. Rack awareness is the concept of choosing the closer DataNode based on rack information.

How many replicas can you have in a Hadoop cluster?

For that Hadoop has some Rack awareness policies. There should not be more than 1 replica on the same Datanode. More then 2 replica’s of a single block is not allowed on the same Rack. The number of racks used inside a Hadoop cluster must be smaller than the number of replicas.

How to implement an external topology script in Hadoop?

If implementing an external script, it will be specified with the net.topology.script.file.name parameter in the configuration files. Unlike the java class, the external topology script is not included with the Hadoop distribution and is provided by the administrator. Hadoop will send multiple IP addresses to ARGV when forking the topology script.