NameNode Recovery Mode for Hadoop Distributed File System

This is for Hadoop eco system like HDFS, Map reduce, Hive, Hbase, Pig, sqoop,sqoop2, Avro, solr, hcatalog, impala, Oozie, Zoo Keeper and Hadoop distribution like Cloudera, Hortonwork etc.
alpeshviranik
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NameNode Recovery Mode for Hadoop Distributed File System

Postby alpeshviranik » Fri Aug 01, 2014 10:05 pm

What is NameNode Recovery Mode? is there any process to recover the corrupt NameNode without Backup? Is it so important to know about it?
Like to know about NameNode Recovery Tools/command for the Hadoop Distributed File System.


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Re: NameNode Recovery Mode for Hadoop Distributed File Syste

Postby Guest » Fri Aug 01, 2014 10:09 pm

We should make sure that manual recovery is almost never necessary. Its always important to know about all data recovery option.
You will configure multiple metadata storage locations. Then, if one storage location is corrupt, you can read the metadata from one of the other storage locations.
So think what can you do if the only storage locations available are corrupt? In this case, there is a special NameNode startup mode called Recovery mode and it will help to recover your data.


the NameNode will interactively prompt you at the command line about possible courses of action you can take to recover your data.

If you don't want to be prompted, you can give the -force option. This option will force recovery mode to always select the first choice. Normally, this will be the most reasonable choice.

Keep in Mind Recovery mode can cause/make you to lose data, you should always back up your edit log and fsimage before using it.

NameNode Recovery command to recover the data
% ./bin/hadoop namenode -recover
At this point, the NameNode will ask you whether you want to continue.

You have selected Metadata Recovery mode. This mode is intended to recover lost metadata on a corrupt filesystem. Metadata recovery mode often
permanently deletes data from your HDFS filesystem. Please back up your editlog and fsimage before trying this!

Are you ready to proceed? (Y/N)
(Y or N)

cloudera link for the NameNode recovery options:
https://blog.cloudera.com/blog/2012/05/ ... le-system/


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