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https://issues.apache.org/jira/browse/HDFS-1940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13033434#comment-13033434
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Rajit commented on HDFS-1940:
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In the abovementioned situation HDFS system was having 4 physical copies of
same data block (blk_1727421609840461376) accross the cluster , 1 datanode was
having 2 copies and another 2 different datanodes were having other 2 different
copies. Now if I remove the file with -rm -skipTrash option only 3 copies of
the data block is getting deleted. Only one copy (latest one , which was copied
manually ) got deleted from the datanode (which had 2 previously)
> Datanode can have more than one copy of same block when a failed disk is
> coming back in datanode
> ------------------------------------------------------------------------------------------------
>
> Key: HDFS-1940
> URL: https://issues.apache.org/jira/browse/HDFS-1940
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: data-node
> Affects Versions: 0.20.204.0
> Reporter: Rajit
> Assignee: Bharath Mundlapudi
>
> There is a situation where one datanode can have more than one copy of same
> block due to a disk fails and comes back after sometime in a datanode. And
> these duplicate blocks are not getting deleted even after datanode and
> namenode restart.
> This situation can only happen in a corner case , when due to disk failure,
> the data block is replicated to other disk of the same datanode.
> To simulate this scenario I copied a datablock and the associated .meta file
> from one disk to another disk of same datanode, so the datanode is having 2
> copy of same replica. Now I restarted datanode and namenode. Still the extra
> data block and meta file is not deleted from the datanode
> ls -l `find /grid/{0,1,2,3}/hadoop/var/hdfs/data/current -name blk_*`
> -rw-r--r-- 1 hdfs users 7814 May 13 21:05
> /grid/1/hadoop/var/hdfs/data/current/blk_1727421609840461376
> -rw-r--r-- 1 hdfs users 71 May 13 21:05
> /grid/1/hadoop/var/hdfs/data/current/blk_1727421609840461376_579992.meta
> -rw-r--r-- 1 hdfs users 7814 May 13 21:14
> /grid/3/hadoop/var/hdfs/data/current/blk_1727421609840461376
> -rw-r--r-- 1 hdfs users 71 May 13 21:14
> /grid/3/hadoop/var/hdfs/data/current/blk_1727421609840461376_579992.meta
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