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From "Harsh J (Resolved) (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (HADOOP-3211) Utility to enforce current replication policy on already exitsting blocks
Date Thu, 29 Dec 2011 05:50:31 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-3211?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Harsh J resolved HADOOP-3211.

    Resolution: Not A Problem

The balancer does this today. The BlockManager and its services do not, however.
> Utility to enforce current replication policy on already exitsting blocks
> -------------------------------------------------------------------------
>                 Key: HADOOP-3211
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3211
>             Project: Hadoop Common
>          Issue Type: New Feature
>            Reporter: Robert Chansler
> If the replica placement policy changes, or if the cluster topology changes, existing
block replicas will not be deliberately moved to implement the new policy or to reflect the
new topology. The re-replicator and the re-balancer always implement the current policy, but
a healthy block may never attract the attention of either of those facilities. 
> In practice, all replicas of a block have been found within a single rack (as allowed
by the previous _random rack_ placement policy. The {{fsck}} facility reports such examples.
> The re-placer utility could follow the model of the re-balancer. Or even be part of the
> An alternative implementation would scan the {{fsck}} report for curious blocks, and
rename a replica block file on the data node, so as to hide it. The re-replicator would be
expected to create a new replica properly placed. (This is a fix up that any administrator
could implement.)
> (1761414)

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