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From "Kartashov, Andy" <Andy.Kartas...@mpac.ca>
Subject a question on NameNode
Date Mon, 19 Nov 2012 14:27:10 GMT
Guys,

I am learning that NN doesn't persistently store block locations. Only file names and heir
permissions as well as file blocks. It is said that locations come from DataNodes when NN
starts.

So, how does it work?

Say we only have one file A.txt in our HDFS that is split into 4 blocks 1,2,3,4 (no replication),
with block 1-2 residing on DN1 and blocks 3,4 on DN2.

When we start NN it reads it metastore and tries to locate and map the locations of 4 blocks
of file A.txt??

Andy Kartashov
MPAC
IT Architecture, Co-op
1340 Pickering Parkway, Pickering, L1V 0C4
* Phone : (905) 837 6269
* Mobile: (416) 722 1787
andy.kartashov@mpac.ca<mailto:andy.kartashov@mpac.ca>

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