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what are the reasons for under replica - why this happens

hi all

 

we have production HDP 2.6.4 cluster , with 12 data nodes machines

from ambari we can see ~25000 number of replica

when this happens then we fix the under replica 

but after some time its return again

 

what we need to check in order to find the root cause for this behavior  

 

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Michael-Bronson
1 REPLY 1

Re: what are the reasons for under replica - why this happens

Expert Contributor

Hi Mike, 

 

It can happen due to multiple reason. Quoting from https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/HdfsDesign.html

The necessity for re-replication may arise due to many reasons: a DataNode may become unavailable, a replica may become corrupted, a hard disk on a DataNode may fail, or the replication factor of a file may be increased

Are you noticing any of these "dataNode may become unavailable, a replica may become corrupted, a hard disk on a DataNode may fail" prior to under replicated state?