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Deploying Hadoop

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  • Q. Why do master nodes normally require a higher degree of fault tolerance than slave nodes?

  • A. Slave nodes are designed to be implemented on commodity hardware with the expectation of failure, and this enables slave nodes to scale economically. The fault tolerance and resiliency built into HDFS and YARN enables the system to recover seamlessly from a failed slave node. Master nodes are different; they are intended to be “always on.” Although there are high availability implementation options for master nodes, failover is not desirable. Therefore, more local fault tolerance, such as RAID disks, dual power supplies, etc., is preferred for master nodes.

  • Q. What does JBOD stand for, and what is its relevance for Hadoop?

  • A. JBOD is an acronym for “Just a Bunch of Disks,” which means spinning disks that operate independently of one another, in contrast to RAID, where disks operate as an array. JBOD is recommended for slave nodes, which are responsible for HDFS block storage. This is because the average speed of all disks on a slave node is greater than the speed of the slowest disk. By comparison, RAID read and write speeds are limited by the speed of the slowest disk in the array.

  • Q. What are the advantages to deploying Hadoop using a commercial distribution?

  • A. Commercial distributions contain a “stack” of core and ecosystem components that are tested with one another and certified for the respective distribution. The commercial vendors typically include a management application, which is very useful for managing multi-node Hadoop clusters at scale. The commercial vendors also offer enterprise support as an option as well.

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