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From Manjunath A <manjunath.tec...@gmail.com>
Subject Re: General Query : Master & DataNode start
Date Wed, 04 Jan 2017 03:05:40 GMT
Hi Renjith,

As per your setup description I assume you have one master node (namenode)
and 2 datanodes. Please find answers below:-

1) If one datanode gets stopped or suspended, the heartbeat between the
datanode and master gets stopped and then namenode(master) takes care of
finding the next appropriate available datanode to replicate the lost
blocks and will automatically trigger replication and hence maintains the
replication factor. For more details you can check the below link:-
https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/HdfsDesign.html#Data_Disk_Failure_Heartbeats_and_Re-Replication

2) If you have properly configured the master in master.txt and slaves in
slaves.txt inside the <hadoop-dir>/etc/hadoop/ directory and if you have
made sure ssh connectivity works fine between master and datanodes then all
you have to do is run start-all.sh in the master node and the framework
takes care of starting the datanode instances in the datanode servers on
its own .

Thanks,
Manjunath

On Tue, Jan 3, 2017 at 9:46 AM, Renjith Gk <renjithgk@gmail.com> wrote:

> Hi All,
>
> As part of my lab exercise i am doing a self study of Hadoop. i have
> cloned Master to 2 Datanodes as Datanode 1 and Datanode 2.
>
> Two Querys from Real Scenarios :
>
> 1. If Master is Up and running, DataNodes are stopped/suspended, will
> there be any communication channel from Datanode to Master or will the
> replication works ?
>
> 2.. Is there a need to run this command start-dfs.sh or start-all.sh in
> master as well as datanodes ?
>
> Thanks,
> Renjith
>

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