HBASE-15332 Document how to take advantage of HDFS-6133 in HBase
(cherry picked from commit e0a656ed50027a7d982f1eca7a8c0ee3cab47f92)
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@ -1347,6 +1347,28 @@ Settings for HDFS retries and timeouts are important to HBase.::
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Defaults are current as of Hadoop 2.3.
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Check the Hadoop documentation for the most current values and recommendations.
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The HBase Balancer and HDFS Balancer are incompatible::
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The HDFS balancer attempts to spread HDFS blocks evenly among DataNodes. HBase relies
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on compactions to restore locality after a region split or failure. These two types
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of balancing do not work well together.
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+
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In the past, the generally accepted advice was to turn off the HDFS load balancer and rely
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on the HBase balancer, since the HDFS balancer would degrade locality. This advice
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is still valid if your HDFS version is lower than 2.7.1.
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+
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link:https://issues.apache.org/jira/browse/HDFS-6133[HDFS-6133] provides the ability
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to exclude a given directory from the HDFS load balancer, by setting the
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`dfs.datanode.block-pinning.enabled` property to `true` in your HDFS
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configuration and running the following hdfs command:
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+
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----
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$ sudo -u hdfs hdfs balancer -exclude /hbase
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----
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+
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NOTE: HDFS-6133 is available in HDFS 2.7.0 and higher, but HBase does not support
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running on HDFS 2.7.0, so you must be using HDFS 2.7.1 or higher to use this feature
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with HBase.
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.Connection Timeouts
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Connection timeouts occur between the client (HBASE) and the HDFS DataNode.
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They may occur when establishing a connection, attempting to read, or attempting to write.
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