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The following page has been changed by KonstantinShvachko: http://wiki.apache.org/lucene-hadoop/FAQ ------------------------------------------------------------------------------ If you find something that you wish were done better, and know how to fix it, read HowToContribute, and contribute a patch. + == 5. If I add new data-nodes to the cluster will HDFS move the blocks to the newly added nodes in order to balance disk space utilization between the nodes? == + + No, HDFS will not move blocks to new nodes automatically. However, newly created files will likely have their blocks placed on the new nodes. + + There are several ways to rebalance the cluster manually. + 1. Select a subset of files that take up a good percentage of your disk space; copy them to new locations in HDFS; remove the old copies of the files; rename the new copies to their original names. + 2. A simpler way, with no interruption of service, is to turn up the replication of files, wait for transfers to stabilize, and then turn the replication back down. + 3. Yet another way to re-balance blocks is to turn off the data-node, which is full, wait until its blocks are replicated, and then bring it back again. The over-replicated blocks will be randomly removed from different nodes, so you really get them rebalanced not just removed from the current node. +
