You decide to create a cluster which runs HDFS in High Availability mode with automatic failover,
using Quorum Storage. What is the purpose of ZooKeeper in such a configuration?
A.
It only keeps track of which NameNode is Active at any given time
B.
It monitors an NFS mount point and reports if the mount point disappears
C.
It both keeps track of which NameNode is Active at any given time, and manages the Edits file.
Which is a log of changes to the HDFS filesystem
D.
If only manages the Edits file, which is log of changes to the HDFS filesystem
E.
Clients connect to ZooKeeper to determine which NameNode is Active
Explanation:
http://www.cloudera.com/content/cloudera-content/clouderadocs/CDH4/latest/PDF/CDH4-High-Availability-Guide.pdf(page 15)
Must be A
For reliable ZooKeeper service, you should deploy ZooKeeper in a cluster known as an ensemble. As long as a majority of the ensemble are up, the service will be available. Because Zookeeper requires a majority, it is best to use an odd number of machines. For example, with four machines ZooKeeper can only handle the failure of a single machine; if two machines fail, the remaining two machines do not constitute a majority. However, with five machines ZooKeeper can handle the failure of two machines.
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more details to proof that A is correct
http://www.cloudera.com/content/cloudera/en/documentation/cdh5/v5-0-0/CDH5-High-Availability-Guide/cdh5hag_hdfs_ha_software_config.html
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A is correct and edit file is maintain by journal node.once active name node down zookeeper is responsilbe for failover however journal maintain edit log file,stand by name node refer this jounal node file once it become active.
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Correct answer A
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I choose A
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