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MapReduce >> mail # user >> RE: a question on NameNode


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Re: a question on NameNode

Am 19.11.2012 um 15:43 schrieb "Kartashov, Andy" <[EMAIL PROTECTED]>:

> So, what if DN2 is down, i.e. it is not sending any blocks’ report.  Then NN (I guess) will figure out that it has 2 blocks (3,4) that has no home and that (without replication) it has no way of reconstructing the file A.txt. It must spit the error then.

One major feature of HDFS is its redundancy. Blocks are stored more than once (three times by default), so chances are good that another DataNode will have that block and report it during the safe mode phase. So the file will be accessible.

Kai

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Kai Voigt
[EMAIL PROTECTED]