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From Abirami V <abiramipand...@gmail.com>
Subject Re: Query regarding the replication factor in hadoop
Date Fri, 19 Sep 2014 13:26:18 GMT
You  will get under replicated block and missing replicas when you run hdfs
fsck /

you may see info like the following

Under replicated blk_-4791859336845413240_1544. Target Replicas
is 3 but found 2 replica(s).



On Fri, Sep 19, 2014 at 5:36 AM, adarsh deshratnam <
adarsh.deshratnam@gmail.com> wrote:

> 1. *How hadoop will take care of balancing of replicas as the required
> replicas are 3 , but we have only 2 data nodes up and running.*
>
> *Ans:* As here the replication factor is three. The data block will be
> replicated three time within 2 nodes. Block replication is random.
>
> *2. What happens when we try to write new  data into hdfs at this point of
> time ? whether the write would be successful with only 2 data nodes and
> replication factor 3 or it returns any error message?*
> *Ans:*It will write successfully.
>
>
> For further info please refer below link:
> http://hadoop.apache.org/docs/r1.2.1/hdfs_design.html
>
>
> Thanks,
> Adarsh D
>
> On Fri, Sep 19, 2014 at 5:46 PM, Raghavendra Chandra <
> raghavchandra.learning@gmail.com> wrote:
>
>> Hi All,
>>
>> I have one very basic query regarding the replication factor in HDFS.
>>
>> Scenario:
>>
>> I have 4 node cluster : 3 data nodes and 1 master node.
>>
>> The replication factor is 3. So ideally each data node would  get one
>> replica .
>>
>> Assume that meanwhile one of the data node went down.
>>
>> so ideally we will be having 2 data nodes.
>>
>> Queries:
>>
>> 1. How hadoop will take care of balancing of replicas as the required
>> replicas are 3 , but we have only 2 data nodes up and running.
>>
>> 2. What happens when we try to write new  data into hdfs at this point of
>> time ? whether the write would be successful with only 2 data nodes and
>> replication factor 3 or it returns any error message?
>>
>>
>> These queries might be simple, but it would be really helpful if some one
>> can answer.
>>
>> Thanks and regards,
>> Raghav Chandra
>>
>>
>

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