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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3292) When a block is severely under replicated at creation time, a request for block replication should be scheduled immediately
Date Tue, 22 Apr 2008 00:31:21 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12591138#action_12591138
] 

dhruba borthakur commented on HADOOP-3292:
------------------------------------------

When a client gets a new block from the namenode, it can tell the namenode the number of replicas
of the previous block that it successfully wrote to. If this number is smaller than the target
replication factor for the file, the namenode can immediately schedule replication for it,

> When a block is severely under replicated at creation time, a request for block replication
should be scheduled immediately
> ---------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-3292
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3292
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: Runping Qi
>
> During writing a block to data nodes, if the dfs client detects a bad data node in the
write pipeline, it will re-construct a new data pipeline, 
> excluding the detected bad data node. This implies that when the client finishes writing
the block, the number of the replicas for the block 
> may be lower than the intended replication factor. If the ratio of the number of replicas
to the intended replication factor is lower than
> certain threshold (say 0.68), then the client should send a request to the name node
to replicate that block immediately.

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