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Subject: Re: how to select  the position of a block
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From: Harsh J <harsh@cloudera.com>
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Moving discussion to hdfs-dev.

DataNodes report disk usage (space) and current transfer thread counts =
(load) periodically to the NameNode. NameNode uses this information to =
make a decision while building the pipeline DNs for your client request. =
I believe the class is called something like ReplicationTargetChooser =
(off the top of my mind), and you can take a look at the logic involved =
there in selecting any form of node (isGoodTarget or summat). Then work =
your way downwards to see how the information flows.

On 07-Dec-2011, at 8:36 AM, =E9=83=AD=E5=86=B2 wrote:

> Hadoop:The Definitive Guide  said that when the client is out of the =
cluster, hadoop will select the storage position of a block randomly,but =
it will not select the datanode which is too busy or too full.
>=20
> so i want to kown that  how hadoop judge or measure a datanode is full =
or not?