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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HDFS-550) DataNode restarts may introduce corrupt/duplicated/lost replicas when handling detached replicas
Date Mon, 17 Aug 2009 23:40:14 GMT

     [ https://issues.apache.org/jira/browse/HDFS-550?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Hairong Kuang updated HDFS-550:
-------------------------------

    Description: 
Current trunk first calls detach to unlinks a finalized replica before appending to this block.
Unlink is done by temporally copying the block file in the "current" subtree to a directory
called "detach" under the volume's daa directory and then copies it back when unlink succeeds.
On datanode restarts, datanodes recover faied unlink by copying replicas under "detach" to
"current".

There are two bugs with this implementation:
1. The "detach" directory does not include in a snapshot. so rollback will cause the "detaching"
replicas to be lost.
2. After a replica is copied to the "detach" directory, the information of its original location
is lost. The current implementation erroneously assumes that the replica to be unlinked is
under "current". This will make two instances of replicas with the same block id to coexist
in a datanode. Also if a replica under "detach" is corrupt, the corrupt replica is moved to
"current" without being detected, polluting datanode data. 

  was:
Current trunks calls first unlinks a finalized replica before appending to this block. Unlink
is done by temporally copying the block file in the "current" subtree to a directory called
"detach" under the volume's daa directory and then copies it back when unlink succeeds. On
datanode restarts, datanodes recover faied unlink by copying replicas under "detach" to "current".

There are two bugs with this implementation:
1. The "detach" directory does not include in a snapshot. so rollback will cause the "detaching"
replicas to be lost.
2. After a replica is copied to the "detach" directory, the information of its original location
is lost. The current implementation erroneously assumes that the replica to be unlinked is
under "current". This will make two instances of replicas with the same block id coexist in
a datanode. Also if the replica under "detach" is corrupt, the corrupt replica is moved to
"current" without being detected, polluting datanode data. 


> DataNode restarts may introduce corrupt/duplicated/lost replicas when handling detached
replicas
> ------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-550
>                 URL: https://issues.apache.org/jira/browse/HDFS-550
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.21.0
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>            Priority: Blocker
>             Fix For: Append Branch
>
>
> Current trunk first calls detach to unlinks a finalized replica before appending to this
block. Unlink is done by temporally copying the block file in the "current" subtree to a directory
called "detach" under the volume's daa directory and then copies it back when unlink succeeds.
On datanode restarts, datanodes recover faied unlink by copying replicas under "detach" to
"current".
> There are two bugs with this implementation:
> 1. The "detach" directory does not include in a snapshot. so rollback will cause the
"detaching" replicas to be lost.
> 2. After a replica is copied to the "detach" directory, the information of its original
location is lost. The current implementation erroneously assumes that the replica to be unlinked
is under "current". This will make two instances of replicas with the same block id to coexist
in a datanode. Also if a replica under "detach" is corrupt, the corrupt replica is moved to
"current" without being detected, polluting datanode data. 

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